The 5-Minute Back Boiler Replacement Cost Guide


Welcome to our 5-minute guide to back boiler replacement cost guide.

We’re going to go through everything from what a back boiler is, what your replacement options are, as well as the average cost of replacing a back boiler with a combi boiler.

If you’ve still got questions regarding your back boiler replacement, leave a comment at the end and we’ll reply as soon as we can.

What Is A Back Boiler?

Back boilers are a heating and hot water system integrated into your chimney behind a gas fire. If you’ve got central heating and can’t see your boiler, but do have a fireplace, you’re likely to have a back boiler.

Why Do Houses Have Back Boilers?

Back boilers date back to the 1960s when they were the latest technology. Like combi boilers today, they became very popular. They were fitted up until the early 80s. After that, regular, system and combi boilers took over. Today, the most popular choice of heating is the combi boiler.

Should You Replace A Back Boiler With A Gas Boiler?

If you want an efficient system that saves you money on utility bills then a back boiler isn’t going to help you with that. They are not very energy efficient. Replacing a back boiler with a new A-rated boiler will save you money in the long run. Many of the newer boilers have an energy rating of well over 89% efficiency.

If a back boiler breaks down, it’s usually doesn’t make economic sense to spend more money on repairs. Some of the back boilers still installed in UK homes are more than 40 years old and most of the parts have deteriorated and will require replacement or repair very soon anyway.

Back Boiler Removal Costs

Your back boiler will need to be removed. If you have an existing central heating system linked to the back boiler, the cost of removing the back boiler is likely to be around £500. This includes removal of the old boiler, removing redundant pipework and tanks, and capping off pipework where necessary.

Back Boiler Replacement Costs

When replacing a back boiler your system will be upgraded, meaning it will be converted from one system to another. In this case, it will mean concerting your current, non-efficient back boiler into an energy efficient boiler. The fuel type could be gas, LPG, electric or oil. The system set-up could be regular, system or combi. We discuss the different options in more detail below.

Cost Of Replacing A Back Boiler With A Combi

If you’re swapping a back boiler to a new combi boiler, the cost will be around £2,650. Read more: Cost To Swap Back Boiler To Combi Boiler

The above cost assumes taking out the back boiler, hot water tanks and redundant pipework and fitting a new premium A-rated boiler.

Cost Of Replacing A Back Boiler With A Regular, Or System Boiler

If you’re swapping a back boiler to a regular or system boiler, the cost will be around £2,450. Read more: Cost To Swap Back Boiler To System Or Regular Boiler

The above costs assume that you’re fitting a premium, A-rated system or regular boiler.

Replacing A Back Boiler, In A New Location

Back boiler replacement costs don’t just consist of the new boiler. The boiler will need a new flue to vent the flue gases from inside the boiler to outside air. A back boiler uses the chimney to expel this air, whereas new boiler use either horizontal or vertical flues.

A horizontal flue goes through a wall straight to outside. If your boiler isn’t on an outside wall, you might need flue extensions to ensure it is long enough to go outside.

A vertical flue passes through a roof. If a boiler is located in a loft or other roof space it will most likely have to pass through the roof because it usually won’t be able to pass through an outside wall. Sometimes extensions can have flat roofs and you might elect to have your flue passing through the flat roof.

Access is sometimes an issue and scaffolding might be needed – this can add considerable expense to an already expensive boiler installation. That’s why it’s very important to plan your new boiler location.

Most of the time, the boiler will go in a utility room, garage, airing cupboard or another location where it can be hidden out of the way, rather than being in the way.

If the only free space is your kitchen cupboard, most manufacturers design boilers that are small enough to fit inside – they cost a little more than the bigger alternative but they tuck away pretty nicely.

The Worcester Greenstar 25Si, Worcester Greenstar 30Si, Vaillant ecoFIT pure 825 and the Vaillant ecoFIT pure 830 are some of the combi boilers that will fit into kitchen cupboards.

Typically, you will pay an additional £300-500 to move your boiler to a new location during the replacement of your current back boiler.

Back Boiler Replacement Costs (Full Central Heating Installation)

Many properties around the UK would benefit from a full central heating upgrade. If you currently have a back boiler then it’s likely your pipework is 40-50 years old. This could mean parts of it need upgrading if there are signs or wear and tear or leakages.

So, how much does back boiler replacement cost, including all pipework?

There’s no straightforward answer. The price varies from property to property. However, for a typical 3-4 bedroom property with 10 radiators, all pipework and a new A-rated boiler, it’s likely to cost around £5,000.

The above is a good guideline. The difficulty with laying pipework, the size and number of radiators you want, the make and model (and type) of boiler you want, will all contribute to the final cost.

N.B. If you want to replace your back boiler with a ‘system’ boiler you’ll have the additional cost of a new cylinder and some additional pipework.