If you are asking this question, your boiler has probably just given you a scare, and you want a straight answer rather than a sales pitch. Here it is: a straightforward like-for-like combi boiler swap in the UK typically costs somewhere in the £1,200 to £3,500 range fully fitted, according to MyJobQuote’s boiler installation cost guide. Moving the boiler, upgrading the flue, or fitting a system or conventional boiler instead of a combi can push that higher. The only way to know your actual number is a proper survey and a written quote, but this guide explains what moves the price so you are not going in blind.
What actually affects the cost
The headline price you see quoted online is a starting point, not a promise. A boiler engineer pricing your job will factor in:
- The type of boiler. A combi is usually the cheapest to fit because it does not need a separate hot water cylinder or tank. System and conventional boilers cost more in parts and labour.
- Output size. A one-bathroom flat needs a smaller, cheaper boiler than a four-bedroom house with two bathrooms running at once.
- Where it is going. A like-for-like swap in the same spot is the cheapest option. Moving the boiler to a new room, or running a new flue route through an external wall, adds labour and materials.
- Brand and warranty length. Longer manufacturer warranties (10 to 12 years versus 2 to 5) usually come with a higher unit price, but can be worth it if you plan to stay in the property.
- Extras. A new filter, a smart thermostat, a power flush of your existing radiators, or bringing old pipework up to current standards can all add to the final bill.
Combi vs system vs conventional: which costs more?
| Boiler type | Relative cost | Best for |
|---|---|---|
| Combi | Lowest, no cylinder or tank needed | Most homes, flats, 1 to 2 bathrooms |
| System | Mid range | Homes needing multiple bathrooms at once |
| Conventional | Highest, cylinder plus loft tank | Larger or older homes already plumbed for one |
A combi boiler heats water on demand and does not need a cylinder or loft tank, which keeps both the unit cost and the installation labour down. It is the most common choice in UK homes and usually the cheapest overall.
A system boiler uses a hot water cylinder but no cold water tank in the loft. It costs more than a combi but suits homes with higher hot water demand, since it can supply multiple bathrooms at once without the pressure drop a combi can suffer.
A conventional (regular) boiler needs both a cylinder and a loft tank, and is the most expensive to install from scratch, though it is often the right choice for larger, older properties already plumbed for one.
If your home is not connected to the mains gas network, an oil-fired boiler is a common alternative, and it must be fitted by an engineer registered with OFTEC rather than Gas Safe.
Is it worth getting multiple quotes?
Yes, and it matters more than most homeowners think. Boiler pricing varies significantly between installers for the same job, partly because of brand relationships and stock, and partly because some quotes are padded and some are not. Getting two or three like-for-like quotes, in writing, with the same boiler brand and output specified, is the single easiest way to avoid overpaying. It is also how you judge who actually surveyed your job properly rather than guessing over the phone.
When you are comparing installers, check they are registered on the Gas Safe Register (it is a legal requirement, not a nice-to-have), and look at how they are reviewed independently rather than just the testimonials on their own website. That is exactly the process we use to build our Top 5 lists, so browsing a page for your town is a fast way to shortlist installers who have already been checked.
How do I know if I need a new boiler at all?
Not every problem means replacement. A few signs it is genuinely time to start budgeting for a new one rather than another repair:
- It is over 10 to 12 years old, which is roughly the point where parts availability and efficiency both start working against you.
- You have called an engineer out more than once or twice in the past year for the same or different faults.
- It is losing pressure repeatedly, or making banging and gurgling noises that a service has not resolved.
- A repair quote is creeping close to half the cost of a full replacement.
If none of that applies, a service and a proper diagnosis from a Gas Safe engineer is almost always cheaper than jumping straight to a new unit.
Frequently asked questions
How much does a new combi boiler cost fitted?
A straightforward like-for-like combi swap typically costs somewhere in the £1,200 to £3,500 range fully fitted, including labour, a basic flue and a standard warranty. More complex jobs, bigger homes, or higher-output boilers push that up. Always get a fixed, written quote rather than relying on a phone estimate.
Is it cheaper to repair a boiler or replace it?
A repair is almost always cheaper up front. But if your boiler is over 10 to 12 years old, has needed more than one or two call-outs in the past couple of years, or a repair quote is edging toward half the cost of a new one, replacing it usually makes more financial sense over the next few winters.
Do I need a Gas Safe registered engineer to fit a boiler?
Yes. It is a legal requirement in the UK for anyone installing or working on a gas boiler to be Gas Safe registered. Always ask for their Gas Safe ID card and check the registration number on the Gas Safe Register before work starts.
How long does a new boiler installation take?
A straightforward like-for-like swap usually takes a single working day. Moving the boiler to a new location, upgrading the flue route, or fitting a larger system can take two to three days.
About the author
Stu Clark
Stu spent over 15 years in the trades, working as a plumber before running his own plumbing and bathroom renovation company with a team of eight. He founded Top5Trades to give homeowners the kind of shortlist and straight advice you would get from someone who has actually done the work. More about us →