Replacing a boiler in London typically costs £1,050 to £4,800 fully fitted, depending on the type of replacement, the boiler’s size, and the brand you choose. A straightforward like-for-like combi swap sits at the lower end of that range. Converting to a system boiler, moving the unit, or replacing an old back boiler pushes costs toward the top.
That’s the honest short version. The problem with most cost guides is they stop there, leaving you with a range wide enough to be almost useless — £1,800 to £10,000 doesn’t tell you what your specific job will cost. This guide breaks the number down properly: by boiler type, by brand, by size, and by exactly what drives the price up or down, so you can spot a fair quote when you see one.
Quick Answer: Average Boiler Replacement Cost in London
| Replacement Type | London Price Range | What Drives It |
|---|---|---|
| Like-for-like combi | £1,050 – £2,500 | Same boiler type, same position, existing pipework reused |
| Combi to system conversion | £3,500 – £5,500 | New cylinder, new pipework runs |
| System boiler replacement | £4,000 – £6,800 | Existing pipework, new boiler + cylinder |
| Regular (conventional) boiler | £1,800 – £5,000 | Depends on cylinder and tank condition |
| Boiler relocation | +£300 – £800 | Added to any replacement type above |
National averages for a straightforward combi swap sit around £2,300 to £2,700. London prices typically run £400 to £800 higher than the national average once labour, parking and access are factored in.
How Much Does a Combi Boiler Replacement Cost?
A combi boiler replacement in London starts from £1,050 for a straightforward like-for-like swap, where the new unit goes in the exact same spot as the old one. This is the most common and most affordable type of boiler replacement, since no new pipework, cylinder, or flue rerouting is involved.
Combi boilers heat water on demand rather than storing it, which is why they suit flats and homes with one bathroom particularly well. If you’re simply swapping an ageing combi for a modern equivalent, expect your quote to land toward the lower end of the London price range — assuming your existing pipework is in reasonable condition and doesn’t need upgrading.
How Much Does a System Boiler Replacement Cost?
Replacing an existing system boiler and cylinder together typically costs from £4,000 in London. System boilers work alongside a hot water cylinder, storing pressurised water rather than heating it instantly, which suits homes with two or more bathrooms used at similar times.
If you already have a system boiler and cylinder and you’re simply replacing both with modern equivalents, the job is faster and more predictable than a first-time conversion, since the pipework routes and cylinder location already exist. Converting from a combi to a system boiler for the first time costs more — typically from £3,500 — because new pipework has to be run to wherever the cylinder is going.
How Much Does a Regular (Conventional) Boiler Replacement Cost?
A like-for-like regular boiler replacement typically costs £1,800 to £5,000, depending heavily on the condition of the existing cylinder and loft tank. Regular boilers, sometimes called conventional or heat-only boilers, work with both a cylinder and a cold water feed tank, usually in the loft.
These are increasingly rare in new installations, since most homes replacing an old regular boiler switch to either a combi or a modern system boiler instead. If you’re keeping a regular setup rather than switching type, the price depends mainly on whether the existing tank and cylinder are being reused or replaced alongside the boiler.
Boiler Replacement Cost by Brand
Brand affects both the upfront unit cost and the length of warranty you get. Based on current London supply-and-fit pricing:
| Brand | Typical Fitted Price Range | Positioning |
|---|---|---|
| Baxi | £1,799+ | UK-manufactured, mid-range, widely serviced |
| Ideal | £1,599 – £1,949 | Best-selling UK brand, wide model range |
| Glow-worm | £1,599+ | Most budget-friendly major brand |
| Worcester Bosch | £1,699 – £2,699 | Premium, strong reputation for period properties |
| Vaillant | £2,049 – £2,599 | Premium, longer standard warranties |
Worcester Bosch and Vaillant are consistently recommended for London’s period housing stock, largely due to compact sizing and reliable performance in older properties with tighter installation spaces. Baxi and Ideal sit in the mid-range, offering solid reliability without the premium price tag. Glow-worm is the most cost-effective major brand, suited to straightforward flats and smaller homes.
Boiler Replacement Cost by Size (kW Output)
Boiler size is driven mainly by your number of bathrooms, not bedrooms — a common misconception. Here’s roughly what each output level costs to have fitted in London:
- 24kW combi: From £1,399 — suits flats and 1-2 bedroom homes with one bathroom
- 25kW–28kW combi: From £1,499 — suits 2-3 bedroom homes with one bathroom
- 30kW combi: From £2,029 — suits larger homes or two bathrooms with moderate simultaneous use
- 35kW+ or system boiler: From £2,499 — suits homes with two or more bathrooms in regular simultaneous use
Choosing a bigger boiler than you need doesn’t improve performance — it just costs more upfront and can lead to inefficient short-cycling. A free boiler size calculator is a faster way to get this right than guessing based on bedroom count alone.
What Else Affects Your Boiler Replacement Price?
Beyond boiler type, brand and size, several other factors move the final number:
- Labour costs. London Gas Safe engineers typically charge more than the national average due to higher living costs, parking, and congestion charge zones.
- Gas pipe upgrades. Modern high-efficiency boilers need higher gas flow than older models. Properties with narrow internal gas pipes, common in pre-1970s London housing, sometimes need this upgraded, which isn’t always flagged until survey stage.
- Boiler relocation. Moving the boiler to a different room typically adds £300 to £800 on top of a standard replacement.
- Flue rerouting. Changing where the flue exits the building adds cost and time versus reusing the existing route.
- Old pipework condition. Corroded or non-compliant pipework sometimes needs replacing alongside the boiler itself.
Is It Cheaper to Repair or Replace a Boiler?
Repair is usually cheaper in the short term, but replacement often makes more financial sense once your boiler passes a certain age or breakdown frequency. As a rough guide:
- Repair first if: the boiler is under 10 years old, it’s a single specific fault (no heating, an error code, low pressure), and the repair quote is well under half the cost of a new boiler.
- Replace instead if: the boiler is over 10-12 years old, you’ve had more than two repairs in the past year, or a single repair quote approaches half the price of a new unit.
Common repair costs for context: a circulating pump typically costs £230 to £390 to replace, a PCB (control board) £290 to £580, and a full heat exchanger £480 to £880. If you’re facing a heat exchanger replacement on an older boiler, that’s usually the point where replacement becomes the more sensible option.
What’s Included in a Proper Boiler Replacement Quote?
A complete, honest quote should include all of the following — if any are missing or vague, ask before booking:
- The boiler unit itself, supplied and fitted
- Removal and disposal of your old boiler
- A digital thermostat
- A magnetic filter and system flush
- Copper pipework connections
- Your Gas Safe certificate
- Manufacturer warranty registration
Anything not on this list — a smart thermostat, radiator upgrades, a power flush, or pipework replacement — should be itemised separately so you know exactly what you’re paying for.
How Long Does Boiler Replacement Take?
Most boiler replacements are completed within a single day. A like-for-like combi swap typically takes 4 to 6 hours. A system boiler conversion, involving new pipework and a cylinder, usually takes 1 to 2 days. Jobs combining boiler relocation or flue rerouting can extend to 2 days depending on complexity.
Can I Get a Fixed-Price Boiler Replacement in London?
Yes, and it’s worth insisting on one. Many companies advertise a low “from” price and only confirm the real total after a home visit, by which point you’re less likely to walk away. A genuinely fixed price, confirmed before the engineer arrives rather than adjusted on the day, protects you from that pattern. Our <a href=”https://boilerinstallerlondon.uk/boiler-replacement-london/”>boiler replacement pricing</a> is structured this way — fixed per job type, confirmed with a short assessment rather than negotiated on your doorstep.
Frequently Asked Questions
How much does it cost to replace a boiler in London?
Boiler replacement in London typically costs £1,050 to £4,800 fully fitted, depending on whether it’s a like-for-like swap, a conversion, or a full system replacement.
What is the average cost of boiler replacement in London?
The average cost for a standard combi replacement in London is around £2,300 to £2,700, though a straightforward like-for-like job can cost less, from £1,050 with some installers.
How much does it cost to replace a combi boiler?
A combi boiler replacement starts from £1,050 for a like-for-like swap, rising with boiler size and brand — larger 30kW+ combis typically cost £2,000 or more fitted.
How much does it cost to replace a system boiler?
Replacing an existing system boiler and cylinder together typically starts from £4,000. Converting from a combi to a system boiler for the first time starts from £3,500.
How much does a Worcester Bosch boiler replacement cost?
Worcester Bosch boiler replacement in London typically costs £1,699 to £2,699 fitted, depending on the model and output.
Is it cheaper to repair or replace a boiler?
Repair is usually cheaper short-term for boilers under 10 years old with a single fault. Replacement becomes more cost-effective once a boiler passes 10-12 years old or needs repeated repairs.
What is included in a boiler replacement quote?
A proper quote includes the boiler unit, old boiler removal, a digital thermostat, magnetic filter, system flush, pipework connections, and your Gas Safe certificate.
How long does it take to replace a boiler?
Most replacements take a single day. A like-for-like combi swap takes 4 to 6 hours; a system boiler conversion takes 1 to 2 days.
Can I replace my boiler without changing the radiators?
Yes. In most cases, existing radiators in good condition connect to a new boiler without needing replacement, unless they’re corroded, leaking, or undersized for the room.
Are boiler replacement prices higher in London than the rest of the UK?
Yes, typically £400 to £800 higher than the national average for an equivalent job, mainly due to higher labour costs, parking charges, and congestion zone fees.
Getting a Real Price, Not a Guess
The honest answer to “how much does it cost to replace a boiler in London” depends on three things: the type of replacement, the size you actually need, and the brand you choose — not your postcode alone. A fair quote should separate these clearly rather than burying them in a wide, unhelpful range.
If you’d rather skip the guesswork, send us your current boiler type and postcode on WhatsApp and we’ll confirm your exact replacement category and fixed price before you commit to anything. You can also browse our fixed-price combi boiler packages to see exact costs by model before speaking to anyone.