A new gas boiler, fitted in the place of the old one, typically costs £1,800 to £4,000. Most of that goes on the boiler and a day or two of an engineer's time. The rest depends on the flue, the controls and how clean the heating system is.
New boiler cost by job size
Typical UK cost of replacing a gas boiler, by job size
| Job size | Typical cost | What it usually looks like |
|---|---|---|
| Small | £1,800–£2,500 | Like-for-like swap, same position, same flue |
| Typical | £2,500–£3,300 | A higher-output unit, new controls, a system clean and a filter |
| Large | £3,300–£4,000+ | An awkward flue, a vertical or extended flue, a cylinder or plume kit |
The tiers divide the £1,800–£4,000 guide for gas boiler replacement. Replacing one boiler with another in the same spot is the cheapest kind of job, because the gas supply, radiators and most of the pipework stay where they are.
What is in the price
- The boiler, and its flue kit if the old one can't be reused.
- Taking the old boiler out and removing it from the house.
- Connecting the gas, flow, return and condensate pipes.
- A system clean and a filter, where the quote includes one.
- Commissioning, a test of the gas and safety devices, and the paperwork.
- A warranty, whose length and conditions vary by manufacturer.
Why two quotes for one house differ
Mostly it comes down to which boiler and how much is bundled in. A mid-range boiler with a standard warranty is a different product from a premium one with a longer guarantee, and some installers include controls and a filter while others price them as extras. Ask each engineer to say which model, which flue and which extras they've allowed for.
If a quote is far below the others, find out what has been left out before you get excited. Make sure the engineer is on the Gas Safe Register, because a cheap job done by someone who isn't is the worst bargain on offer.
A bigger boiler isn't automatically better. An oversized unit costs more to buy and can run less efficiently, so ask the engineer why they've chosen the output they have.
If you're unsure whether to replace or keep patching, our guide on the signs you need a new boiler is a good place to start. For a quick estimate for your own house, use the boiler cost calculator.
Frequently asked questions
How much does a new gas boiler cost fitted?
Typically £1,800 to £4,000. A like-for-like swap is nearer the bottom, and an awkward flue or extra work pushes it up.
Can my existing radiators stay when the boiler is replaced?
Usually yes. A replacement normally reuses the radiators and most of the pipework, though a system clean is often recommended first.
How long does a boiler replacement take?
Allow around one to two days. Moving the flue or finding hidden problems can add time.
Is the cheapest quote the best option?
Not necessarily. Compare the boiler model, flue, extras, warranty and the engineer's Gas Safe registration, not only the total.
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