DATA-BACKED GUIDE · UPDATED JULY 2026
Combi boiler replacement cost: swap vs conversion
If your combi has finally given up, the good news is a like-for-like replacement is usually the simplest heating job going. The price shifts a lot, though, depending on whether you are swapping one combi for another or converting from an old system with a tank. The real prices below are drawn from genuine prices so you can gauge what your own job might run to.
The quick version
- A like-for-like combi boiler swap is the cheapest route because the pipework is largely already in place.
- Converting from a system or conventional setup to a combi costs more, as tanks and cylinders come out and pipework changes.
- The boiler make, output size and warranty length all move the final figure.
- Relocating the boiler adds flue and pipe runs, so keeping it where it is keeps costs down.
What people actually paid
Real prices, in people's own words
- £2,000“a 30kw one at a cost of £2k January 2021”
- £2,000“£2k”
- £2,400“I recently had a Worcester boiler installed (no other work, just a new boiler) and that was £2400 on it's own (including VAT and labour).”
- £2,500“just paid 2500 for a new combi (similar cost boiler)”
- £2,500“just paid 2500 for a new combi”
- £3,500“We paid £3500 to have a new boiler fitted and the old back boiler removed for my mum”
Genuine amounts posted publicly. We publish the price and the quote, never the person.
Why the price varies so much
The biggest single factor is whether it is a swap or a conversion. Replacing an old combi with a new combi in the same place is quick, so labour is lower. Going from a conventional boiler with a hot water cylinder and cold tank over to a combi boiler means removing that kit, capping off, and reworking pipes, which is a bigger day or two of work. On top of that, the brand and output you choose, the condition of your existing radiators and pipework, and whether the system needs a power flush all shift the total. As with most trades, a national firm usually quotes above a local installer for identical work.
How to pay less
- Ask installers to price a like-for-like combi boiler swap first before considering any relocation.
- Get at least three Gas Safe quotes and make sure each lists the same boiler model and controls.
- Question whether a power flush is genuinely needed or whether a cheaper chemical clean will do.
- Compare independent local engineers against national brands, since the local quote is often lower.
Common questions
Is replacing a combi cheaper than converting to one?
Yes. A like-for-like combi boiler replacement reuses most of the existing pipework, so it is faster and cheaper. Converting from a tank-and-cylinder system to a combi involves stripping out the old kit and reworking pipes, which adds a day or more of labour. The real prices below show both.
What size combi boiler do I need?
It depends on the number of radiators and bathrooms and how much hot water you use at once. A larger output suits a busy family home, while a smaller flat needs less. A Gas Safe engineer will size it properly rather than guessing, which avoids paying for more boiler than you need.
Can I replace a combi boiler myself?
No. It is illegal to fit or replace a gas boiler unless you are Gas Safe registered. Beyond the legal side, incorrect work risks gas leaks and carbon monoxide, and it will void the manufacturer warranty. Always use a registered engineer and keep the certificate.