A combi boiler installation typically costs £2,200 to £5,000. A combi heats hot water as you use it, so there's no cylinder and no loft tank. That is the appeal. It's also why the price swings: swapping one combi for another is simple, while converting a house that has tanks and a cylinder is a bigger job.
Combi installation cost by job size
Typical UK combi boiler installation cost, by job size
| Job size | Typical cost | What it usually looks like |
|---|---|---|
| Small | £2,200–£3,000 | A combi replacing a combi, existing pipework reused |
| Typical | £3,000–£4,000 | A swap from a regular or system boiler, tanks left in place or partly removed |
| Large | £4,000–£5,000+ | A full conversion, tanks and cylinder removed, new gas pipe and flue |
These tiers divide the £2,200–£5,000 guide for combi boiler installation. The top tier can be exceeded when the gas pipe or flue needs significant new work.
What a conversion involves
- Draining and removing the hot water cylinder and the loft tanks, or capping them off.
- Reconfiguring the pipework so the boiler feeds the radiators and the taps directly.
- Checking the gas pipe is big enough to supply a combi at full output.
- Re-routing the flue if the new boiler sits in a different place.
- Making good the airing cupboard or loft afterwards, which is sometimes left out of a quote.
A combi isn't right for everyone
A combi relies on your incoming mains water. If the pressure and flow are weak, or if several people regularly run showers at once, it may disappoint. Ask the engineer to measure the flow rate before you commit. Our boiler types guide explains where a system or regular boiler still makes more sense.
Always confirm the installer is on the Gas Safe Register and ask for the quote to list every part of the conversion, including who makes good the cupboard. A quote that only names the boiler isn't enough to compare.
A combi can't store hot water, so two taps running at once share what the boiler can heat. If that describes your household, say so when you request quotes.
To see a range for your own job, try the boiler cost calculator.
Frequently asked questions
How much does a combi boiler installation cost?
Typically £2,200 to £5,000. Swapping a combi for a combi is at the bottom, and converting from a regular or system boiler costs more.
Will a combi improve weak mains water flow?
No. A combi uses the incoming mains, so weak flow is usually still weak. Ask the engineer to measure it before you decide.
Do I have to remove the hot water cylinder?
Normally, yes, because a combi replaces it. The tanks and cylinder can be removed or capped off, and the quote should say which.
How long does a combi installation take?
Around one to three days. A conversion takes longer than a straight swap.
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