Short answer: The cost of a new boiler in London depends on the boiler type, whether it stays in the same place, how the flue and condensate run, the gas pipe size, the state of the old system, the controls England's Boiler Plus rules require, and access in flats and terraces. A fair price can only be confirmed after a survey.
People search “how much is a new boiler london” more than almost any other boiler question. We do not publish prices, because a fair quote depends on the home. What we can do is explain what changes the price, so you can compare quotes properly. A boiler installation is always priced after a survey.
The main things that change the price
| Factor | Why it matters |
|---|---|
| Boiler type and size | A combi, system or regular boiler; output matched to the home |
| Changing type | Going from a tank and cylinder to a combi means removing tanks and changing pipework |
| Boiler location | Same spot is simpler; moving it needs new gas, water, flue and drain |
| Flue route | Straight out of a wall is simple; up through a roof or across a ceiling void is not |
| Condensate route | Inside to a waste pipe, or outside to a drain |
| Gas pipe size | A pipe too small for the boiler must be upgraded |
| System clean | Old systems often need cleaning before a new boiler goes on |
| Controls | England’s Boiler Plus rules set minimum controls |
| Scale protection | Needed in hard water areas under BS 7593 guidance |
| Access | Flats, stairs, parking and building rules in London |
| Making good | Filling holes, boxing in, decorating |
Changing boiler type
Many older north London houses still have a regular boiler, with a cold water tank in the loft and a hot water cylinder in an airing cupboard. Swapping to a combi frees up space, but it is a bigger job than a like for like swap. Tanks come out, pipes change, and the hot water now relies on mains flow. Our guide on combi or system boilers explains which suits which home.
The flue in London homes
The flue carries exhaust gases outside. In a terrace it usually exits through the back wall. In a mid terrace with a side return, the position has to keep clear distances from windows, doors and boundaries. In flats, the flue may need to cross a ceiling void before it reaches the outside. HSE guidance means a flue hidden in a void must have inspection hatches so it can be checked; if it cannot be inspected, an engineer will class the boiler as “At Risk”. See the HSE flues in voids bulletin and our guide on boiler flue rules.
Camden, Islington and Hackney have large numbers of conservation areas. Islington alone has 42 conservation areas. Where a flue would show on a front wall, some owners check with the council’s planning team first.
Gas pipe size
A new boiler needs enough gas. In older houses, gas pipework has often been extended many times. If the existing pipe from the meter is too small or too long for the new boiler, it has to be upgraded. This is checked at survey, not guessed. Our page on gas pipework covers this work.
System clean and water treatment
A new boiler on an old dirty system can block up fast. BS 7593, the standard for heating water, sets out cleaning the system, adding inhibitor and fitting a filter. North and east London water is hard: Thames Water’s 2025 reports give averages from about 258 to 278 mg/l across the area. Guidance says scale protection should be fitted where hardness is over 200 ppm. Our guide on a power flush or chemical clean explains the cleaning options.
Controls required in England
The Boiler Plus rules have applied since April 2018. Every new gas boiler needs a timer and room thermostat. A new combi needs one more energy saving measure from this list: flue gas heat recovery, weather compensation, load compensation, or smart controls with automation and optimisation. Some boilers meet this with their own controls. Others need an add on.
Paperwork and alarms
A new boiler must be notified to the local authority within 30 days by the Gas Safe registered business that fitted it. You then get a Building Regulations Compliance Certificate, as Gas Safe Register explains. Approved Document J also requires a carbon monoxide alarm where a new or replacement fixed gas appliance is installed.
Access in London
Access affects how long a job takes. Things that come up in our area:
- flats on upper floors with no lift
- controlled parking zones where a permit or a pay bay is needed
- boilers in lofts with no fixed ladder or boards
- leasehold flats where the freeholder must agree to a new flue through an outside wall
- blocks with rules on working hours
Tell the surveyor about any of these. See our Hackney area page for the mix of flats and terraces there.
Comparing quotes
When you have more than one quote, check each one lists:
- the exact boiler make, model and output
- where the boiler, flue and condensate will go
- whether a system clean, inhibitor, filter and scale reducer are included
- which controls are included for Boiler Plus
- whether a carbon monoxide alarm is included
- who registers the boiler for its warranty
- the Gas Safe registration number of the business
Gas work in the UK must be done by a Gas Safe registered engineer. Ask to see the ID card and check it lists a domestic boiler category.
Quick questions
Why do new boiler quotes vary so much?
Quotes cover different work. One may include a system clean, a filter, a scale reducer and smart controls, and another may not. Compare the full list of what each quote includes.
Is it cheaper to keep the boiler in the same place?
Usually. Moving a boiler means new gas pipe, new water pipes, a new flue route and a new condensate drain. Keeping the same spot often avoids most of that.
Do I need a survey before a quote?
Yes. The flue position, the gas pipe size and the condition of the system can only be checked at the property. A quote without a look is a guess.
Last updated 23 October 2026. Written for homes in London. Rules can change, so check the linked sources for the latest position.