Back Boiler Replacement Cost – Complete Guide

Back boilers are a technology that is very much of their time. If you have a back boiler that is reaching the end of its life, the chances are you will be looking to replace it with a more modern boiler. In this short guide, we will tell you what your best options are and make some suggestions on where you can find the best deals.

If you have a back boiler in your home, it is probably safe to assume two things. It is very old and approaching the end of its useful service life, and you want to replace it with a modern combi boiler.

If you have settled for a back boiler all this time, you are probably wondering what you need to do to replace it when the time comes. That’s what this guide is all about.

Over the next five minutes or so, we will tell you everything you need to know about replacing a back boiler, including how to save money on the best possible deals through an online installation site like WARMZILLA.


What Is A Back Boiler?

If you are not sure what a back boiler is, it is a rather dated technology that involves integrating your boiler into the back of your gas fire.

If your home has hot water and central heating plus a gas fire, but you can’t find a boiler anywhere, it is quite likely you have a back boiler.

Back boilers were all the rage in the 1960s when the technology first emerged and they were being installed well into the 1980s before modern regular and combi boilers took over.

If your property still has a back boiler it is likely to be decades old and highly inefficient. We would strongly recommend upgrading to a new modern combi boiler.

Why You Should Replace A Back Boiler With A Gas Boiler?

Back boilers are old and this means they are inefficient. If you are running your home on a back boiler, the chances are that you could save a significant amount of your utility bills by upgrading to a combi boiler or even a regular gas boiler.

Another consideration is repairs. Getting replacement parts for a back boiler is almost impossible these days and many qualified engineers may well have never even set eyes on one before.

Their age means deterioration is inevitable and it is only a matter of time before your back boiler gives up the ghost.

It is a good idea to get a replacement boiler put in now, to avoid being left without heating or hot water when your back boiler does finally break down. To get an idea of what a replacement might cost, fill in the form on the WARMZILLA website for a fixed-price quote.

Removal Costs

If you are replacing a back boiler, you will have to remove your existing boiler. This will involve capping pipework and other things and is not especially cheap.

On average, you are likely to have to pay between £600 and £800 to remove and dispose of the old boiler and make everything safe around where it was installed.

When you install a new combi or regular boiler, you will then also have to factor in the costs of added new pipework, flue installation, and other infrastructure to fit this too. This is usually referred to as a system upgrade.

How Much Does A Back Boiler Replacement Cost?

A system upgrade does cost more than installation a conventional new boiler and even moving a boiler to a new location.

No matter what type of new boiler you are installing, the costs will be higher and you should be prepared for that.

The question you probably want answering is exactly how much can you expect to have to pay? This is a tricky question to answer and there are plenty of different factors involved.

#1 – Replacing A Back Boiler With A Combi

If you are simply switching a back boiler for a modern combi boiler, you are likely to have to pay out at least £3,000 including the boiler itself and associated labour costs.

This estimate is based on buying a Worcester Bosch 25i boiler from WARMZILLA and includes all the costs of disposing of your old back boiler and the necessary pipework and flue installation for the new boiler too.

If you choose a more powerful boiler, this figure is likely to rise.

#2 – Replacing A Back Boiler With A Regular Or System Boiler

If you are planning to replace your back boiler with a regular or system boiler, the costs are likely to be similar, again assuming you choose a boiler with the KW power.

The cost of replacing the back boiler fire with a regular or system boiler will be similar to a combi, assuming the same KW boiler is used.

You will pay around £3000 for a 30KW regular installation or system boiler, again with all the associated labour costs included.

#3 – Relocation

You will almost certainly be relocating a boiler if you are upgrading from a back boiler. This involves installing new pipework and a new flue, either through an external wall or vertically up through the roof of your property.

You will need to plan the new location of your boiler carefully, to comply with the latest regulation. Discuss this will your installer in advance to make sure you are compliant.

If you are opting for a combi boiler, you are likely to want to choose a compact model that can be hidden away in a cupboard somewhere.

An example is the Worcester Bosch CDI Compact range or the Ideal Logic Plus.

Boiler relocations typically cost around £300-600, and while this cost should be factored into your system upgrade bill, it isn’t always.

#4 – Full Central Heating Installation

If you have a back boiler to replace, it is likely to be 40 or 50 years old at least. This could mean that the pipework in your central heating system also needs replacing, and possible your radiators too.

The cost of this work will depend on the size of your property and the number of new radiators you need to install.

For a typical 3-4 bedroom property with 8-10 radiators, the cost of replacing the entire central heating system and installing a new A-rated combi boiler is likely to cost around £5,000.

This is a very broad estimate and other possible complications, such as the difficulty of accessing pipework etc. could drive the price higher. If you need new hot water tanks for a regular boiler, expect the figure to be higher still.

How To Save Money When Replacing Your Back Boiler

We always advise you get several quotes whenever you are replacing a boiler and this is no different with a back boiler.

You will need to get an engineer to visit your property to size up the scale of the job and give you an accurate quote. Getting a quote shouldn’t cost you a penny.

We also recommend you get a quote from WARMZILLA. They are an online installation firm that can offer some of the lowest prices on a wide range of high-quality boilers from all the top manufacturers.

Their installation costs are also extremely competitive and they frequently have special offers and discounts available too.

When you do get an engineer round, there are a few things you should discuss with them:

  • Their Gas Safe credentials – this is a big job and requires a fully-qualified engineer.
  • Where the flue will go – this has to be in line with current safety guidelines.
  • The right boiler – choose the right sized boiler for your property, with a long warranty.
  • Fixed price quote – always make sure your quote is a fixed price to avoid any unexpected increases.
  • Boiler filters – make sure get boiler filters installed, especially if you are sticking with your old central heating system.


If your property has a back boiler it is almost certain to be decades old and you will probably want to replace it.

In this short guide, we have explained why it needs replacing and what your options are. We have also gone into more detail about what the likely costs of replacing a back boiler are and why.

We have also made some recommendations on how to save money when replacing a back boiler including getting a quote from WARMZILLA.

Have you ever had to replace a back boiler? Do you have any advice or tips we haven’t covered in this guide? Do you need to replace a back boiler and have some questions we haven’t answered?

We always try to respond to all comments and questions left on our site, so please do leave yours in the comment box below and we will endeavour to get back topo you as fast as we can.

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