Back Boiler Replacement Cost 2026
Replacing a back boiler costs £2,500 to £4,500 depending on whether you go for a combi or system boiler. If you have a back boiler, your heating bills are almost certainly higher than they need to be. These old units run at just 55 to 70% efficiency, while a modern boiler hits 90% or better. Around 1.5 million UK homes still have one tucked behind the fireplace.
£3,000
Combi replacement
£3,500
System replacement
£200-£400
Annual saving
55-70%
Old efficiency
Prices updated April 2026 · Based on industry data and contractor submissions.
Gas Safe registered engineers only. Removing a back boiler and fitting a replacement is gas work that must be carried out by a Gas Safe registered engineer. It is illegal for anyone else to do this work. Always check your engineer's Gas Safe ID card before they start.
Asbestos risk. Back boilers installed before the mid-1980s often have asbestos-containing materials around them. An asbestos survey (£50 to £150) should be carried out before any removal work begins. If asbestos is found, it must be removed by a licensed asbestos removal contractor before the heating engineer can start work.
Quick answer
How much does it cost to replace a back boiler?
A back boiler replacement costs £2,500 to £3,800 for a combi boiler, or £3,000 to £4,500 for a system boiler. That covers removing the old back boiler, fitting the new one (typically in the kitchen), running new pipework, and capping the chimney flue. Budget an extra £200 to £500 for making good the fireplace opening, and £300 to £800 for asbestos removal if needed.
Back Boiler Replacement Prices at a Glance
All prices include supply, installation, and labour by a Gas Safe registered engineer. Fireplace and asbestos costs shown separately.
| Job | Price Range | Average |
|---|---|---|
| Back boiler removal + combi replacement | £2,500 - £3,800 | £3,000 |
| Back boiler removal + system replacement | £3,000 - £4,500 | £3,500 |
| Fireplace making good (basic plaster + surround) | £200 - £500 | £350 |
| New decorative gas fire in existing opening | £800 - £1,500 | £1,100 |
| Asbestos survey + removal (if needed) | £300 - £800 | £500 |
| Flue capping / chimney sealing | £150 - £300 | £200 |
Prices based on industry data for 2026. Your actual cost will depend on your property and what is involved.
Why Replacing a Back Boiler Costs More Than a Standard Boiler Swap
A straightforward boiler swap where the new unit goes in the same spot as the old one is cheaper because the pipework, flue, and controls are already in place. Back boiler replacements involve more work because the new boiler goes somewhere completely different.
The old boiler has to come out of the fireplace
Back boilers are bricked into the fireplace opening and connected to a chimney flue. Removing one means carefully dismantling it, disconnecting the gas and water pipework, and clearing out the opening. If asbestos is present, this step alone can add a day and £300 to £800.
The new boiler goes in a different location
Modern boilers cannot go behind a fireplace. They are wall-mounted units that need a balanced flue through an external wall. The kitchen is the most common spot, but it could be a utility room or airing cupboard. New pipework needs to be run from the old radiator circuits to the new boiler location.
The chimney or flue needs sealing
Once the back boiler is out, the chimney needs capping or the flue liner needs removing and the opening sealing. This prevents draughts and damp getting in. A proper cap with ventilation costs £150 to £300.
The fireplace needs making good
You are left with a hole in the wall where the back boiler sat. At a minimum, this needs plastering and finishing. Some people fit a decorative fire or a feature surround. Others seal it up flush with the wall. Basic making good runs £200 to £500.
Back Boiler vs Modern Boiler: The Efficiency Gap
The single biggest reason to replace a back boiler is efficiency. You are wasting a third or more of the gas you pay for with one of these old units.
Back boiler (1960s-1980s)
55-70% efficient. Up to 45p of every £1 on gas is wasted.
Modern condensing boiler (2026)
90%+ efficient. Only 10p of every £1 is lost.
Annual saving: £200 to £400
Switching from a back boiler to a modern condensing boiler typically saves £200 to £400 a year on gas bills. The exact amount depends on the size of your home, how well insulated it is, and how much heating you use. Poorly insulated homes with high gas usage see the biggest savings.
Payback period: 7 to 12 years
At £300 a year in savings against a £3,000 replacement, you are looking at roughly 10 years to break even on the cost alone. Factor in fewer repairs, lower carbon emissions, and a more reliable heating system, and the real payback comes sooner. If ECO4 covers part of the cost, the payback is much faster.
Could ECO4 cover your replacement?
The ECO4 energy efficiency scheme can fund back boiler replacements for eligible households. If you receive certain benefits, have a low household income, or live in an energy-inefficient property (EPC rating D or below), you may qualify for a fully funded replacement. Even without benefits, some households qualify through the LA Flex pathway via their local council. It is worth checking before you pay out of pocket.
Back Boiler Replacement Prices by Region
Labour rates are the main driver of regional price differences. London and the South East are the most expensive, while the North and Wales tend to be cheaper.
| Region | Average Cost | vs National |
|---|---|---|
| London and South East | £3,600 | +20% |
| South West | £3,200 | +7% |
| East of England | £3,100 | +3% |
| Midlands | £3,000 | Average |
| Yorkshire | £2,850 | -5% |
| North West | £2,800 | -7% |
| North East | £2,750 | -8% |
| Scotland | £2,900 | -3% |
| Wales | £2,850 | -5% |
| Northern Ireland | £2,800 | -7% |
Based on industry data. Prices for a back boiler removal and combi boiler replacement, fully installed.
How to Get Your Back Boiler Replaced for Less
Back boiler replacements are not cheap, but there are ways to bring the cost down. The ECO4 tip alone could save you the entire bill.
Check if ECO4 covers you first
The ECO4 scheme can pay for the entire replacement if you qualify. Eligibility depends on your benefits, income, and your home's energy rating. Even partial funding can knock £1,000 or more off the bill. Contact your energy supplier or use the government's Simple Energy Advice service before you commit to paying full price.
Book it for spring or summer
Heating engineers are rushed off their feet from October to January. Book the swap for warmer months when you can manage without heating for a day or two, and engineers have more diary space. You will often get a better price and a quicker turnaround.
Get three quotes and compare the breakdown
Back boiler replacements involve several separate jobs: removal, new boiler fitting, pipework, fireplace making good, and possibly asbestos removal. Prices vary a lot because some engineers include everything while others quote the boiler swap and treat the rest as extras. Ask each one for a full itemised breakdown so you can compare properly.
Keep the fireplace simple
A basic plaster-and-paint finish on the old fireplace opening costs £200 to £500. A decorative gas fire jumps to £800 to £1,500. If your main goal is getting a new boiler for less, keep the fireplace making good as straightforward as possible. You can always upgrade the surround later when the budget allows.
Get an asbestos survey before work starts
Do not let anyone touch the back boiler until asbestos has been ruled out. An asbestos survey costs £50 to £150 and could save you from a much bigger problem. If asbestos is found, it must be removed by a licensed contractor before the heating engineer can start. Budget an extra £300 to £800 for licensed removal if your back boiler was installed before the mid-1980s.
What to Expect: The Back Boiler Replacement Process
A back boiler replacement typically takes 2 to 3 days. If asbestos removal is needed, allow an extra day. Here is how the job usually runs.
- 1
Survey and asbestos check
A Gas Safe registered engineer visits to assess the back boiler, check the pipework, and plan where the new boiler will go. They should also arrange an asbestos survey if the back boiler was installed before the mid-1980s. A proper survey takes 30 to 45 minutes.
- 2
Asbestos removal (if needed)
If the survey finds asbestos, a licensed contractor removes it before any other work starts. This is usually a separate visit and takes half a day to a full day depending on the extent. The area is sealed off and the waste is disposed of safely.
- 3
Day 1: Remove the back boiler
The engineer drains the heating system, disconnects the old back boiler, and removes it from the fireplace opening. The chimney flue is capped or sealed to prevent draughts and damp.
- 4
Day 1-2: Fit the new boiler
The new boiler is wall-mounted in its new location (usually the kitchen). New pipework is run to connect it to the existing radiator circuits, and a balanced flue is fitted through the external wall. New controls and a thermostat are installed.
- 5
Day 2-3: Commission and make good
The system is filled, pressure-tested, and the boiler is commissioned. The old fireplace opening is plastered and made good (or a new fire/surround is fitted if you have chosen that route). The engineer runs a full heating cycle to check everything works.
- 6
Certification and handover
You receive a Building Regulations compliance certificate and the installation is notified to your local authority. The engineer walks you through the controls and explains the annual servicing schedule needed to maintain your warranty.
Use our boiler cost calculator
Get a personalised estimate for your back boiler replacement based on your property type, location, and heating needs. Takes about 60 seconds.
Try the CalculatorFrequently Asked Questions
How much does it cost to replace a back boiler?
Replacing a back boiler with a modern combi boiler costs between £2,500 and £3,800, with an average around £3,000 in 2026. If you need a system boiler instead, expect £3,000 to £4,500. These prices include removing the old back boiler, fitting the new boiler (usually in the kitchen), and basic making good of the fireplace opening.
Do back boilers contain asbestos?
Many back boilers installed before the mid-1980s have asbestos-containing materials around them, particularly in the flue pipe, rope seals, and insulation panels behind the fire. If your back boiler was fitted between the 1960s and 1985, there is a reasonable chance asbestos is present. A qualified asbestos surveyor can test for it before any removal work begins. Licensed asbestos removal adds £300 to £800 to the total cost.
Can I get a grant to replace my back boiler?
Yes. The ECO4 scheme can cover the full cost of replacing a back boiler for eligible households. Eligibility depends on your benefits status, household income, and the energy efficiency rating of your property. Even if you do not qualify for full funding, partial grants are available. Contact your energy supplier or check the government's Simple Energy Advice service to find out if you are eligible.
What happens to the fireplace when a back boiler is removed?
Once the back boiler is taken out, you are left with an empty fireplace opening that needs making good. The cheapest option is to plaster over the opening and fit a simple surround or mantelpiece, which costs £200 to £500. If you want a decorative gas fire in the existing opening, budget £800 to £1,500. You can also leave the opening as a feature with a log burner effect or seal it up entirely.
How efficient is a back boiler compared to a modern boiler?
Back boilers typically run at 55 to 70% efficiency, meaning 30 to 45% of the energy you pay for is wasted. Modern condensing boilers are 90% efficient or better. That difference translates to noticeably lower heating bills, with most households saving £200 to £400 a year after switching from a back boiler to a modern combi or system boiler.
Written by James Carter, Less.co.uk energy specialist
Last updated: · Pricing based on industry data and verified contractor submissions · Methodology
Ready to replace your back boiler for less?
We're setting up our free quote comparison service. Sign up to our newsletter and we'll let you know the moment it goes live.
Get Notified When Quotes LaunchComing soon. Sign up to our newsletter to be the first to know.
