The 16 step 6,000 word [DEFINITIVE] guide to the perfect boiler installation


There are lots of things to consider when choosing an installer to fit a brand new boiler. I hope to guide you through the process from start to finish. This is quite a difficult task, describing in words what I do every single day, but I’m going to give it a real go. It’s quite a long read, but bear with me, it’s worth it.

Not all of the points will be relevant to your particular installation but this guide will at least give you an idea of what to expect from your new boiler installation and what to expect from an installer coming to your house.

I’m pretty sure there will be lots to add, so if anyone wants to contact me, they’re welcome to. Installers are also welcome to contact me.

OK, let’s begin.

1. Your budget – grants, loans, and other schemes

If your boiler breaks down and you need to fork out for a replacement, you might be able to save money by claiming some sort of grant, or even getting it free – if you’re eligible that is.

There are many boiler grants, eco-schemes, rental schemes and even some companies offering you boilers that claim they pay you back in savings made from the new efficient boiler. So, let’s take a look at a few options to see which is best for you and your budget.

ECO scheme

There’s something called the Energy Companies Obligation (ECO) scheme which is run by the government. Under this scheme, some homeowners and private tenants are eligible to have their inefficient boilers replaced either completely free or have the cost heavily subsidised.

This scheme was set up to help you reduce your carbon footprint by improving the energy efficiency of your home. The scheme also offers other measures you might be eligible for including help with improving insulation.

If you’re part of a low-income family and your boiler is more than 8 years old (which is considered inefficient) then you will qualify.

Unfortunately, because funds are now limited, the criteria is getting a little more strict. To qualify, you need to receive at least one benefit (e.g. income support) and your total household income cannot be more than £20,000. If you’re a tenant, you need to ask your landlord for permission, otherwise, you’ll need to own your own home.

The ECO grant was introduced to help struggling families. The Energy Companies that agreed to help with this scheme are:

  • British Gas
  • EDF Energy
  • EON
  • Npower
  • Scottish Power
  • SSE
  • Utility Warehouse
  • Utilita
  • Ovo
  • Economy Energy
  • Co-operative Energy
  • Extra Energy
  • First Utility

If you’re a customer of one of these companies they should have contacted you already to tell you that you’re eligible. If they haven’t or you’re not a customer of theirs, then you can contact them and ask to find out about ECO scheme. For more advice on this, contact the Energy Saving Advice Service (0300 123 1234), or Home Energy Scotland (0808 808 2282) if you live in Scotland.

Further reading: Energy Companies Obligation and Free Insulation – Green Deal

Affordable Warmth Obligation

You may have heard about the Warm Front scheme but this was replaced by the Affordable Warmth Obligation. It’s part of the ECO scheme and provides help with the cost of replacing or repairing your boiler, as well as help with other energy-saving measures. They also offer advice and tips on other upgrades to your heating.

Are you eligible? Again, you’ll need to be receiving certain grants to qualify and either be renting privately or own your own home. If you’re in social housing you might still be able to get help but, usually, only if heating is being installed for the first time.

To qualify under this scheme your home must have an Energy Performace Certificate (EPC) rating of E or less (i.e. E or F or G). Your EPC rating (or energy rating) can be found on your EPC certificate. If you think you have an EPC but can’t find it then it should be available to download on the Domestic Energy Performance Certificate Register. If you don’t have one but want one, then I am able to carry one out for you.

For more advice on this, contact the Affordable Warmth Scheme England (0300 123 1234), Scotland (0808 808 2282) and Northern Ireland (0300 200 7874). In Wales, the scheme is called Nest and is managed by British Gas (0808 808 2244).

Boiler Scrappage Scheme

The Boiler Scrappage Scheme is no longer available as, unfortunately, all the available money has run out. The scheme was set up to provide money-off vouchers to eligible homeowners allowing them to have their inefficient G-rated boilers replaced.

There are some boiler installation companies that offer a ‘Boiler Scrappage Scheme’ discount but this is just a discount that they are provided personally – and not through the government. So, if you do find installers using the term when trying to sell you the boiler be advised, you still need to get other quotes to compare prices and see what kind of saving you’re really getting, if any.

Flow – a boiler that pays for itself?

You might have heard of Flow, you might not have. They’re a new energy supplier and they launched a new boiler in 2015. So a very new entrant into the boiler market. The boiler works by using its own waste gases to turn a small turbine which in turn generates around 2,000kWh of electricity a year.

Now, that’s not bad at all considering the average UK household uses an average of 3,000kWh. However, because the boiler cannot store the electricity it is producing, it needs to be used at the same time it is being produced. That means you might not be receiving the full benefits of the saving if you have a smaller property, with fewer people living in it, using more electricity than the average household.

Another negative is the price, it retails for a whopping £2,880 and only comes with a 2-year warranty – this is seriously expensive considering a medium sized Worcester or Vaillant boiler will only set you back around £1,200, with at least a 5-year warranty thrown in.

If the upfront cost puts you off then it’s worth noting that Flow do have an option with a no upfront cost where you pay over 5 years. However, it’s rather complicated and best avoided.

Our opinion would be to avoid Flow altogether, it’s not a good option.

Renting a boiler

Believe it or not, you can actually rent a boiler. It works on a pay monthly basis and customers sign up to very lengthy contracts, often 12 years. The thing is, they also sign you up to their servicing contracts and it can cost upwards of £40 per month. Over 12 years this is nearly £6,000 – quite a price to pay if you can’t afford the initial outlay.

Credit card or bank loan

It is normally a bad idea to finance your boiler installation using a credit card or bank loan. Although there are cost benefits to be gained by having a new condensing boiler these will be eaten up when repaying the loan. If your current boiler is in good working order and you are worried about it breaking down you could consider boiler cover. Read our guide on Boiler Cover.

2. Finding an installer – getting 3 quotes

You should aim for 3 quotes from 3 different reputable companies. This is more than adequate to get a good idea of what you want and also give you a chance to ask any questions you may have. Bear in mind that every single installation is different and you’ll need tailored advice which is individual to your property.

Each engineer or company will have their preferred boilers and methods of working. It’s a good idea to bounce around ideas you might have to ascertain whether the replies engineer is giving make any sense to you. Unfortunately, the gas engineer trade has a lot of newly qualified engineers working within it since ‘Fast Track’ type of courses were introduced where it’s possible to be a qualified gas engineer in a matter of a few months.

An experienced engineer will be able to offer you the best solution, the most efficient boiler for your needs and be able to save you money not only in the short term but also in the long run.

How to find someone you trust

It’s quite difficult to find someone you trust enough to hand over, what is, quite a large sum of money, to fit you a new boiler. However, the internet has made finding a reputable and reliable tradesman a lot easier. There’s lots of information you can find about a company online, not least their reviews, either good or bad. Google reviews are hard to fake as they are local and relevant and most of them are from Gmail accounts, linked to Google+ pages – so at least Google has some control over the content and authenticity of those reviews. Take a good look online and judge for yourself if the company looks reliable.

Another way to verify the companies competence is to confirm their Gas Safe registration – this can be done by entering it into the Gas Safe Register. For example, our Gas Safe register number is 300451. If you enter that number on this page, you’ll see our registration. A very important thing to note here is that the lower the number, the older the registration and the more experience the engineer or company will therefore have. We’ve been Gas Safe registered for nearly 11 years for example.

How to work out how long a company has been Gas Safe registered by their number? Here are some rough estimates of how long a company has been registered, it’s hard to know exactly without asking:

Estimated time registered with Gas Safe.
Gas Safe ID number Example Number of years
600000-700000 603411 0-3
500000-599999 551423 3-6
400000-499999 N/A* N/A*
300000-399999 300451 6-12
200000-299999 211863 12+
100000-199999 192688 15+
Below 100000 87022 20+

*Gas Safe do not use 4XXXXX

Asking questions

One thing to stress is you mustn’t be afraid to ask questions if you don’t understand anything or if you disagree with anything. It’s your home and you’re the one spending the money – so don’t be afraid to ask what the process is and why the engineer is recommending something.

Asking a lot of questions can inspire confidence in the engineer depending on their actions and answers and it’s a good way to gauge competence. If you’re unsure which way new pipework will be routed then ask!

Analysing your quotes

Once you’ve got your 3 quotes you need to take a detailed look at them, comparing which one offers you the most value. For the sake of transparency, quotes should be broken down in as much detail as possible. Parts and labour should be listed individually so you can compare what you’re getting charged.

When receiving quotes make sure of the following:

  • all quotes are written
  • all quotes show the final price to pay with no surprises
  • all quotes include VAT*
  • all quotes show a detailed breakdown of prices
  • all quotes detail any warranty or guarantee given
  • all quotes show the companies VAT and Companies House registration number and address
  • all quotes show at least one contact number, preferably a landline office number

*all quotes should show a price including VAT, if a company is not VAT registered it means they are either doing a lot of cash in hand jobs or they just aren’t very busy. Installing just 1 boiler week at a total cost of £1750 (£1200 boiler + £500 labour) would take you over the VAT threshold of £85000 per year meaning you would require compulsory VAT registration. So beware of companies not charging VAT and question how busy they really are.

Signing a contract

Once you’ve agreed on an installer you might be asked to sign terms and conditions that detail work to be done and the price you’ll be charged inclusive of VAT. It is important that you do not hand over any money until the work has been completed and you are happy with everything and know how your boiler and boiler controls work.

Any respectable company will not ask for money upfront for work they haven’t yet done.

3. The current mains water pressure of your system

All cold-mains-fed combi boilers require an adequate amount of water to be delivered to the boiler whilst other cold outlets are also in use (e.g. toilets, washing machine filling etc). So it is vital to check the mains water pressure (before installation) is sufficient to ensure there will be no ongoing problems such as water being drawn away to those other outlets.

Water pressure is measured in a unit called ‘bars’. One bar is enough to force water to a height of about 10 metres – so easily enough to fill a storage tank in the loft of a typical 2 storey house. Most water suppliers promise at least 1 bar to your property boundary – which would be enough for a typical combi boiler installation.

Therefore, the first thing the installer should do before attempting to give you a quote is to test your mains water pressure.

I was at one property a few weeks ago where we measured mains water pressure at around 0.8bar. We advised the customer to fit a certain Vaillant boiler model where the full hot water output could be achieved with a minimum of 0.5 bar of mains water pressure. This boiler would be one of the few boilers that would have been suitable for this customer. In this case, it would have been costly not to check. If you’re interested, I use a tool similar to this to check.

If you live on top of a hill or far away from a reservoir or supply then you’re more likely to have issues with you’re pressure. The average house will have a static pressure of 3 bar or so. Some domestic homes can have as high as 5 or 6 bars of pressure.

Flow rate from your tap

Measuring mains water pressure alone will not provide a complete picture of whether a combi boiler will work well or not, the flow rate is very important as well.

The flow rate is measured from your tap in litres per minute and is dependent on the size, type, and condition of the incoming main. It’s important not to confuse mains water pressure with flow rate.

If your flow rate is less than 10 litres per minute then you have a low flow rate. If your flow rate is 10-15 litres per minute then you have an acceptable flow rate. If your flow rate is above 15 litres per minute then you have a good flow rate.

We’ve been to properties in the past where, for example, other installers have quoted the customer for the installation of a Worcester 42CDi which gives 17.4 litres of hot water per minute. We measured the customers flow rate at only 13 litres per minute. This boiler would have been overkill for this property and a waste of the customer’s money.

If you’re interested, I use a tool similar to this to check.

4. Your current system – layout/design and condition, boiler siting

The layout of your current system and whether you want to keep it the same or upgrade to a different system will have a huge effect on the final cost of the work.

Upgrading your system

If you need to upgrade from a system boiler to a combi boiler, for example, this will be the costliest combi boiler installation. The system layout and pipework will need altering. The hot water cylinder and tanks in the loft will need removing. If you have a back boiler that needs replacing and removing this will add time and expense as well. It can sometimes be difficult to remove a back boiler as it may cause the chimney to weaken.

Rerouting pipework

Rerouting new pipework can add considerable expense as well. Beware of companies taking shortcuts, or indeed, charging more for lifting carpets and floorboards. Also note, there are strict rules regarding how pipework is laid in joists and how far you can cut into them. There is a maximum size the ‘notch’ can be cut in a joist and care should be taken. All pipework should be laid or clipped properly and to current standards, not left hanging loose.

Resiting a boiler

A new extension or a total refurbishment are sometimes reasons why you would have a new boiler installed. If the boiler is in the way of an extension, you’ll want it moved. Sometimes the flue exits the back of the building and might just need repositioning, rather than replacing.

If you’ve got a system boiler and now want to opt for a more efficient combi boiler you might want to free up some space in your loft or airing cupboard. You might consider having the new boiler fitted in a garage or spare bedroom; sometimes the location you decide (e.g. near the gas meter) can save you money.

Feeding new pipework to the new boiler can also take time. It is preferable, but not always possible or cost effective, to hide pipework away under floorboards.

The position of the new flue terminal should also be considered. It must be at east 30cm away from any opening such a sa window or door.

Boiler pluming

Flue gases from condensing boilers are cooler than non-condensing boilers so you’ll be able to see the discharge, particularly in colder weather. This is called pluming. Pluming can be a nuisance if crossing neighbour boundaries so a pluming kit is used to eradicate the issue.

If your boiler flue will exit near to a neighbouring properties window or door or access way and you think that pluming will be an issue then make allowances for this.

Moving furniture

Moving furniture is usually the responsibility of the homeowner or their representative. With your permission, and agreement to accept responsibility for damage or breakages, a responsible company will move furniture and other objects out the way.

Ideally, you should clear all space around the areas where you anticipate access will be required to make life easier for the installer.

5. Your hot water demand – bathrooms, ensuites etc

Your hot water demands will usually determine the ideal boiler for your property. Even the smallest 24kW combi boiler can handle up to 14 radiators if installed property – this is more than enough for a typical 3 bedroom property.

So, attention must be made to how much hot water your household is using and how much it could use in the future.

Questions we ask when sizing a boiler for a property:

  • how many bathrooms does your property have?
  • how many separate showers does your property have
  • how many showers or bathrooms will you be adding in the near future?

If you’re considering going up into the loft and adding an ensuite bedroom or extending to the side of the house in the near future, then you should consider a bigger boiler than your current demands dictate.

If you have an ensuite bathroom as well as a main bathroom you’ll sometimes be using the two showers at the same time. A few combi boilers can just about handle the hot water demand but only just about. It’s likely you’ll have a system or regular boiler in your property.

Smaller combi boilers deliver 9-11 litres per minute – it’s not great but it is adequate for a smaller property and a decent enough shower. The bigger models will deliver 16 litres or more of hot water – enough for a powerful shower, and be able to handle a larger number of radiators on the heating side.

A bigger boiler will also be able to fill a bath much quicker than a smaller boiler – it can get annoying waiting for a huge bath to fill with hot water.

6. Choosing a boiler

Choosing a boiler can be a really difficult task. There are a lot of manufacturers and to confuse things further, each manufacturer has a lot of different models to choose from. We’ve compared prices on 63 boilers and surveyed 3,100 homeowners on what they consider the best combi boiler – check out our full guide: Combi Boiler Prices.

We’ve also reviewed which boiler is best for your house, check out our guide: Best Boilers in 2018.

You can either go with our advice and research from the 3,100 respondents or go with your installers choice of boiler. Every installer will have their own preferred boiler, one that they’ve installed the most, repaired the most and consider best overall.

Cheaper boiler or better guarantee?

It’s worth noting that a budget boiler is, in our opinion, a false economy. If you consider the difference between the total installation price of a budget boiler is only a few hundred pounds cheaper than the total installation price of a premium boiler then it doesn’t make sense for a few reasons.

The labour cost for installing a boiler will not change, regardless if it is a cheap or premium boiler. So for the sake of a few hundred pounds, you will be losing out on all the reliability a better brand offers. You’ll also receive a far shorter guarantee, 2 years for a budget boiler as opposed to up to 10 years for a premium boiler.

We’ve worked that boiler cover costs a between £176.40 to £258 annually, check our full guide; Boiler Cover so either you’ll be paying a company for cover, or you’ll be taking a risk with a boiler breakdown. Our survey suggested that the average cost of a boiler repair is £194.

Our recommendation will always be a premium boiler that we trust and have full confidence in. We have experience installing all of the models listed in this guide.

7. Upgrading your pipework – gas and water pipework

As of 1st April 2005, any newly fitted gas-fired boiler in England or Wals must be a condensing boiler with a SEDBUK efficiency rating of either A or B. This means that if your current boiler (the one you are replacing) was installed before that, it won’t be a condensing boiler and might need some pipework alterations or upgrades.

A combi to combi boiler swap

Older gas-fired combi boilers (those installed pre-April 2005) were non-condensing and required only a 15mm copper gas supply pipe to make it run efficiently and safely. Newer, condensing boilers (installed after April 2005) usually require a 22mm copper gas supply pipe to make them run efficiently and safely – this is because they require gas at a higher pressure to be able to run at their most efficient.

Therefore, if your current gas-fired combi boiler was installed after Apri 2005 you will already have upgraded 22mm gas pipework running from the gas meter to the boiler and you won’t have to worry about any pipework modifications if you are after a simple combi boiler to combi boiler replacement. This, of course, assumes your current boiler was installed correctly.

Some exceptions

There are some exceptions where a condensing boiler will work perfectly fine with a 15mm copper gas supply pipe. However, they are few and far between. If your boiler is very close to the gas meter and you don’t have other gas appliances in the property then it could be possible to have a working, safe boiler running on 15mm copper gas supply pipe.

However. a lot of manufacturers now state that they require a minimum of a 22mm copper gas supply pipe to comply with their warranty. You will also be limited as to the number of additional gas appliances you are able to add to the installation at a later date – e.g. a new gas fire or gas hob installation might not be possible without upgrading the pipework first.

How to check

Your installer will first need to check the working pressure at the gas meter. To do this he or she will connect a manometer to the gas meter test nipple. They will then need to operate all gas appliances at full rate – gas boiler on maximum, gas fire on maximum and gas hob with at least 3 rings ignited. A working pressure for the boiler (at the meter) will then be displayed on the manometer.

This test is then repeated but with the manometer attached to the boiler inlet test point. A working pressure for the boiler (at the boiler) will then be displayed on the manometer.

If the difference between these two readings is more than 1mb (one millibar) then the pipework is undersized and potentially dangerous – and so should be upgraded. Take a look at this interesting Money Saving Expert thread on the subject.

Gas pipe sizing is a must for all new combi boiler installations and will ensure you are paying for and installing the correct sized gas pipework for your current setup and your future needs. The calculations and formulas used, however, are sometimes complicated and some installers, unfortunately, take a ‘guess’ that 22mm pipework will be OK.

A system to combi upgrade

If you have a regular or system boiler (i.e. a boiler that also uses a cylinder, hot water tank, expansion tank in the loft) and want to convert to a new condensing and efficient combi boiler then additional pipework modifications will need to be made. Often the hot water tank is in the landing cupboard or bathroom or other inconvenient place and you might want it out of the way.

Your new combi boiler can be sited in a place that suits your current living arrangements. You might have room in your garage or prefer the boiler tucked away in a bathroom closet or up in the loft. The installer will be able to help you decide on a suitable location.

It’s important to note that a new gas supply would need to be run from the gas meter to the new boiler location and this could involve a lot of work depending on the route taken – that’s why it is usually preferable cost-wise to locate the new boiler as near to the gas meter as possible. It is also important to note that some of the hot water pipework needs to be rerouted away from the, now removed, hot water tanks and connected back to seal the system.

Whichever installation you require, always ensure you are happy with the route the pipework will take and how it will look aesthetically. Running gas pipework on the outside of a house doesn’t look good and we don’t advocate the practice – it is lazy and it just doesn’t look good.

Gas pipework passing through a wall

Just so you are aware, gas pipework passing through a wall should be sleeved so it is protected and take the shortest route through the wall. This is quite easy for you to check.

8. Adding a magnetic filter

A magnetic filter is a device that helps collect sludge (all the nasty stuff) from your central heating and boiler. Sludge is made up of rust particles caused by corrosion to the inside of your radiators and pipework. The filter uses a large magnet that attracts these tiny particles and keeps them away from your boiler. A magnetic boiler, in effect, keeps your system clean and your boiler healthy.

Why would I need one?

Simply put, to protect your system. Your system corrodes and sludge is produced. This can block up the boilers heat exchanger and it can be costly to fix. A new Worcester Bosch heat exchanger assembly can cost almost £400 and it would also need fitting adding further cost. Sludge also blocks radiators – some of your radiators might be cold at the bottom or the top because of sludge.

Does it work? Yes, pretty well. Sludge is ferrous in nature (meaning it contains iron) and so it can be trapped by a powerful magnet. However, sludge can also occur from non-ferrous metals such as copper, zinc or aluminium components, and because this is non-ferrous, the magnet will not catch these particles.

To counteract this, your installer should dose your system with a corrosion inhibitor. This is usually done once towards the end of the installation. This stops the inside of your system corroding and, on older systems, negates the needs for a magnetic filter.

Why do I need a magnetic filter on a combi boiler?

Your new comb boiler should be dosed with inhibitor and be fitted with a magnetic filter. This is because newer boilers have heat exchangers with very narrow tubes which are designed to speed up the transfer of heat. These heat exchangers are more prone to blockages and a filter is, therefore, a good idea.

A magnetic filter is not a legal requirement, nor is the requirement to add corrosion inhibitor. However, some manufacturers routinely check if inhibitor has been added to your system if you call them to attend a breakdown in your guarantee period. They use a sampling kit to test whether inhibitor is present, and if it’s not, they can refuse your repair AND keep your call out deposit.

Our advice is to flush the system of all the nasty stuff. Then add corrosion inhibitor and a magnetic filter.

Testing whether your system has corrosion inhibitor

You can easily test whether your central heating system has any corrosion inhibitor added to it. Either buy this kit online and follow the instructions in this video or do it yourself at home. Collect a small amount of water from the bleed valve from your radiator. Add a steel nail and a copper coin to the water and leave it for a week. If the nail starts to corrode, the same corrosion will be taking place on the inside of your central heating system. It’s probably why your water isn’t as hot as it should be or why your radiators have cold spots.

Which magnetic filter is best?

There are a few different magnetic filter manufacturers. The popular makes are Adey Magnaclean, Fernox, Sentinel, and Fernox. Worcester Bosch also manufactures and sells their own brand.

The installer will recommend his own choice of magnetic filter.

9. Adding thermostatic radiator valves

Thermostatic radiators valves (TRV’s), whilst not a legal requirement when having a new boiler replaced, are a great idea. They work by sensing the air temperature next to the radiator and turning the flow of hot water to the radiator either on or off. Interestingly, they don’t actually work like a tap where you can restrict the hot water flow and slow it down. So there’s no proportional control and this is often misunderstood by the general public.

If you’re using the manual valves to control your radiator (the valves with the ‘+’ or ‘-‘ signs) then you probably don’t realise that you’re not controlling (or reducing) the temperature of the radiator – you’re actually reducing the flow of the water through the radiator. If you’re turning the wrong valve then you’re probably causing problems with how the system is ‘balanced’ and might have some radiators not hot enough and others too hot. An installers job, having fitted new central heating, is to balance the system. If the wrong valves are turned this can sometimes cause problems.

If you’re thinking of having TRV’s fitted then it’s best to have them fitted at the same time as having the boiler fitted. Otherwise, at a later date, you’ll pay for the system to be drained down a second time and you’ll have to pay for corrosion inhibitor a second time.

10. Adding a room thermostat

The Boiler Plus initiative was launched in April 2018 by Business, Energy & Industrial Strategy. The standard means that it is an explicit requirement for a timer and a room thermostat to be fitted when having a new gas or oil boiler installed in England.

if you’re having a new gas-fired combi boiler installed then there is also an additional legal requirement to install (at least) one of the following:

  • flue gas heat recovery system
  • weather compensation
  • load compensation
  • smart control featuring automation and optimisation functions

There is also now a legal requirement to ensure installers only fit (in England) domestic gas boilers which have a minimum 92% ErP – roughly a third of boilers on the market fall short of this requirement.

The government are hoping that this will cost the average homeowner an additional one-off payment of about £50 and that the saving could be made back through lower energy bills.

My opinion is that this policy is good news for installers who already consider time and temperature control to be an essential part of a heating system. Making this a mandatory requirement should ensure all installers follow best practice so customers benefit through lower bills and added convenience.

11. Adding additional radiators

If you’re considering additional radiators to your system now would be a great time to have them fitted. Some of your radiators might be old, inefficient or have leaks. They might be clogged up with sludge and not heating up properly due to internal corrosion. You might not have a radiator in your usable loft space and want one there or you might want to swap a single radiator for a double radiator. Whatever your needs, your installer should be able to help you.

What size radiator do I need for my room?

There are calculations that your installer will be able to make based on your room specification and he or she will be able to recommend the correct size radiator. It’s not good enough to simply guess the size when a simple calculation taking a few minutes will give you an exact size.

If you want to size up your own radiator then you’ll need this BTU calculator, and the height, width, and length of the room, as well as the type of glazing in the room.

12. Power flushing your system or flushing your system

Powerflushing – probably the biggest and most expensive con going and a subject that really bugs me. I’ve never come across a system that ever needed a power flush and I have never power flushed a system and I doubt I ever will.

What is power flushing?

Power flushing is a process by which a powerful machine is used to flush the system of debris, rust, and sludge. A high flow / low-pressure water pumping unit is attached to the central heating system, and chemicals are pumped around the system. Power flushing costs between £350 and £500 with British Gas definitely being the most expensive.

There have been lots of articles on the dubious subject of power flushing, here’s a link to a few of them:

If your installer is pushing you towards getting a power flush I would be very wary of using them.

What is a system cleanse

All boiler manufacturers state in their installation manuals that a central heating system should be fully cleaned and flushed out before installing a new boiler. None of them, to my knowledge, ask for a power flush as a mandatory requirement.

If a system is pre-treated with chemicals to soften the sludge and dissolve any limescale build up, then simply draining the system down and flushing through with water at normal pressure is all that is needed. Building Regulations also state that a system should be thoroughly cleaned and flushed out before a new boiler is installed.

Why a system cleanse is vital

Apart from being a legal requirement under Building Regulations, a system cleanse is important to ensure the manufacturer’s guarantee remains valid. If you think of it in terms of buying a new car, it’s unlikely you would use the oil from your old car to run your new engine. Debris, rust, and other contaminants can damage your new boiler and reduce its efficiency.

The heat exchanger, one of the main components of the boiler, can become clogged and restricted which could mean poor circulation, poor heat transference, a noisy boiler and a higher risk of a boiler breakdown. The pump can also get filled with debris affecting its performance.

Boiler manufacturers who offer long parts and labour guarantees will attend your boiler breakdown and if they suspect your system has not been chemically cleansed, they can refuse to honour the guarantee in accordance with their terms and conditions. As mentioned above, it’s a simple test to prove or disprove the presence of inhibitor.

Sentinel and Fernox are the more popular makes of inhibitor. Your quote should definitely include the name of the inhibitor and the price for a chemical system cleanse.

13. Commissioning your system / filling in the Benchmark checklist

In 1999 the Benchmark scheme was launched. This scheme set out to ensure installers followed best practice and consumers were offered as much protection as possible. Benchmark also places a responsibility on manufacturers to follow best practice and this is why, I think, the UK leads the world in the boiler market – both in terms of size and value.

The Benchmark is filled in once the installers work is done and the boiler needs commissioning. The commissioning consists of a checklist and important parts of that checklist are listed below.

  • boiler make, model and serial number
  • engineer name, address, company, phone and ID number
  • Building Regulations notification number
  • list of controls installed
  • system flushed
  • system cleansed
  • inhibitor used
Central heating:
  • gas rate
  • burner pressure
  • central heating flow temperature
  • central heating return temperature
Combi boiler only:
  • scale reducer used?
Hot water:
  • gas rate
  • burner pressure
  • cold water inlet temperature
  • water flow rate
Condensing boilers:
  • condensate drain
  • condensate pipe
All installations:
  • flue gas analyser readings
  • operation of boiler explained to customer
  • instructions, service record and Benchmark left with customer

Important: failure to properly fill in the Benchmark checklist will invalidate your guarantee.

14. Registering the boiler

Registering the boiler is a must. It lets the manufacturer know when the boiler was installed and who installed it and whether it was installed legally. The installation date will also let the manufacturer know when the guarantee period starts.

Registration of a boiler is usually done online and installers have individual accounts where they sometimes build loyalty points depending on the number of boilers of a particular make they install in a calendar year.

It’s worth noting that some manufacturers will only start a warranty as long as the boiler is installed within 6 months of leaving their factory.

15. Notifying building control

Your new boiler should be up and running now and be offering you peace of mind and warmth. It needs to be registered with the Gas Safe Register (the official registration body for all gas engineers). Once that is done, Building Control is automatically notified and your boiler is officially ‘certified’. You’ll receive a certificate in the post.

When selling a property, a solicitor will sometimes want to know whether the boiler was installed legally – this is proof that it was. A similar thing exists with the electrical installation.

16. Advising the customer on how to get the best efficiency from their boiler

An important part of the commissioning of a boiler is explaining to a customer how the boiler and associated controls work. A new boiler and controls could consist of the following:

  • the boiler itself
  • timer / programmer
  • standard thermostat or smart thermostat
  • magnetic filter
  • scale filter
  • thermostatic radiator valves

The operation and efficient use of these components needs to be explained to the responsible person.

About the author

Avatar for Ajvinder Singh
Ajvinder Singh

Ajvinder Singh holds a BA in Business and Management from the London School of Economics and Political Science. He is a regular contributor to Earth Easy, Green Prophet, and many other green living blogs. As well as holding fellow membership with the National Inspection Council for Electrical Installation Contracting and being on the Gas Safe Register, he is also a fully qualified Domestic Energy Assessor with Elmhurst Energy.

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