Heating & energy
Boiler replacement cost guide
A new boiler is one of the most expensive single purchases in the house, and one of the very few jobs where the law says you must not DIY. This page explains how the job runs, so you know what to expect and what a good installer does.
Updated November 2026. Estimates based on typical UK prices.
Typical installed prices reported by the industry
These are widely reported industry ranges, not a quote. They move with boiler brand, output size, and how much of your existing system needs to change. Always confirm your engineer is Gas Safe registered before booking.
The price
What affects the cost?
- 1
Boiler type
Combi, system and regular boilers all differ in price, and converting from one type to another adds work.
- 2
Output and brand
Higher output boilers and premium brands cost more, but longer warranties can offset it.
- 3
Flue and position
Moving the boiler or running a longer flue adds labour and materials.
- 4
Pipework and system clean
Old systems often need a power flush, magnetic filter and new pipework.
- 5
Controls
Smart thermostats and zone controls are extras but can save running costs.
Be honest with yourself
Can you do this yourself?
You can do
- Choosing the boiler and getting quotes
- Clearing space and access for the engineer
- Fitting a smart thermostat if the engineer says it is compatible
Leave to a pro
- Everything to do with the boiler: removal, installation, flue, gas connection and commissioning
- Gas pipework
- Power flushing the system
The rules
Under the Gas Safety (Installation and Use) Regulations 1998, only a Gas Safe registered engineer can legally install, service or repair a gas boiler in the UK. Installation must be notified to building control, which a Gas Safe engineer does for you.
What to expect
How a boiler replacement runs, step by step
You do not do these steps yourself. Knowing the order helps you check your installer is doing the job properly.
- 1
Get three quotes from Gas Safe engineers
Each engineer should visit, check your existing system and flue, and quote for the boiler, labour and any extras in writing. Ask to see their Gas Safe ID card and check the number on the Gas Safe Register.
- 2
Choose the boiler and booking date
Compare like for like: output, warranty length, controls included, and whether a power flush and magnetic filter are in the price.
- 3
Installation day: the old boiler comes out
The engineer isolates the gas and water, drains the system, and removes the old boiler and flue.
- 4
The new boiler is fitted
The new boiler is mounted, the flue fitted and sealed, and gas, water and heating pipework connected. A magnetic filter is usually added.
- 5
The system is cleaned and refilled
The system is flushed, filled with water and inhibitor, and bled so radiators heat evenly.
- 6
Commissioning and safety checks
The engineer tests gas tightness, flue gas and combustion, then fills in the Benchmark commissioning checklist and shows you how to use the controls.
- 7
Paperwork and warranty
The installation is notified to building control and you receive a compliance certificate. Register the manufacturer warranty, and keep all certificates for when you sell.
Learn from others
Common mistakes to avoid
- Hiring someone who is not on the Gas Safe Register
- Choosing only on price and missing that a flush or filter was left out
- Not asking for the Benchmark checklist and compliance certificate
- Forgetting to register the warranty
Frequently asked questions
How much does it cost to replace a boiler in the UK?
A straightforward like-for-like combi boiler swap typically costs £1,800–£3,000 installed. Moving the boiler, upgrading output, or converting to a different system type pushes this up to £4,000–£7,000+. These are industry-reported ranges, not a quote. Get 2 to 3 quotes from Gas Safe registered engineers for your actual system.
Can I fit my own boiler?
No. Legally, only a Gas Safe registered engineer can install, service or repair a gas boiler in the UK. This applies even if you’re a competent DIYer and even for a like-for-like swap. Working on gas appliances without registration is a criminal offence and, more importantly, genuinely dangerous.
How long does a boiler replacement take?
A like-for-like combi swap usually takes a single day. Moving the boiler, converting system type, or adding a new flue run typically takes 2 to 3 days.
How do I get an accurate price for my boiler replacement?
Get a Gas Safe registered engineer out to survey your current system. They’ll confirm boiler type, output size, flue route and whether a powerflush or pipework upgrade is needed. Get 2 to 3 quotes before booking, and check their Gas Safe registration number on the official register.
Can I replace a radiator myself if I’m not allowed to touch the boiler?
Yes. Swapping a radiator like for like is not notifiable work and does not involve the boiler or gas. See our radiator calculator and step-by-step guide for how it is done.
Ready to plan it?
Add this job to your renovation plan to get the order of work, who to book and a budget you can track.