System boilers
A system boiler heats the radiators directly and stores hot water in a cylinder. The pump and expansion vessel are built in, so there is no tank in the loft. It suits larger homes with more than one bathroom, where several taps run at once.
Who system boilers suit
Suits
- Houses with two or more bathrooms
- Homes with good space for a cylinder
- Buyers who want hot water to several taps at once
Good points
- Hot water to several taps at once
- No loft tanks, so the loft is free
- Works with solar thermal and some heat pump upgrades later
- Mains water supply is not the limit it is for a combi
Watch out for
- Needs room for a cylinder
- More parts and more to service than a combi
- Costs more to fit than a combi swap
What system boilers cost
System boilers typically cost £3,000 (Gas system boiler, like-for-like swap, fitted, hot water cylinder not included), with most jobs between £2,500 and £3,500. That includes VAT at 20%. Fitting takes 1–2 days on site.
What you would actually pay
Typical Gas system boiler, like-for-like swap, fitted, hot water cylinder not included · UK- Typical installed cost System boilers, supplied and fitted
- £2,500
- VAT at 20% Standard rate
- £500
- Net cost to you
- £3,000
If you borrowed £3,000.00 over 36 months at 0.0%, it would cost £83.33 a month – £3,000.00 in total, of which £0.00 is interest. The last payment would be £83.45.
Illustration only – not a quote, not an offer of credit, and not financial advice. Rates depend on your circumstances and creditworthiness.
Where the money goes on system boilers
| Element | Typical range |
|---|---|
| Boiler and fitting, like for like A new gas system boiler fitted in place of the old one. The price assumes the cylinder and pipework stay. This row is the headline price and covers the range. | £2,500 – £3,500 |
| Moving the boiler New pipework and a flue route where the boiler moves. Optional, and the labour grows with the distance. | £600 – £1,000 |
| Flue extension, per metre A longer flue run where the new boiler sits further from the outside wall. Priced per metre of flue. | £70 – £120 |
| Power flush Cleaning the radiators and pipework before the new boiler goes on. Optional, and worth asking about on an old system. | £400 – £1,000 |
| Magnetic filter Catches the iron sludge that wears out a boiler, and many manufacturers ask for one under their warranty terms. | £110 – £310 |
Guide prices including VAT. Your actual cost depends on your home, access and specification.
What moves the price of system boilers
- The boiler itself
Budget ranges cost the least, mid-range ranges sit in the middle, and premium ranges with longer warranties cost the most. Output matters less to the price than the range does.
- Like for like or a conversion
Swapping a boiler for the same type in the same place is the cheapest job. Changing type, moving the boiler or re-routing the flue adds pipework, labour and days.
- The state of the system
Old radiators and pipes full of sludge can need a power flush, new valves or a filter before the installer will fit a new boiler under warranty.
- Where you live
Installer rates are higher in London and the South East than in the North and in Scotland, and the regional pages show the difference.
- Who fits it
National installers and local Gas Safe engineers quote differently for the same boiler. Compare quotes on the make and model, the warranty and what is included, not on the headline price alone.
What a quote for system boilers should include
If a quote is missing any of these, ask why before you compare it with another.
- The make, model and output of the boiler, and the length of the manufacturer warranty once it is registered
- Whether the price includes a magnetic filter, a system clean or flush, and the cost if the installer finds the system needs one
- Whether the flue, the condensate pipe and any new pipework are included, and what a longer or relocated flue adds
- Removal and disposal of the old boiler, and who registers the installation with Gas Safe and the manufacturer
- A fixed price in writing, the deposit and the payment schedule, and the workmanship guarantee
- The date, the number of engineers and how many days the heating and hot water will be off
System boilers prices by region
Labour is most of the difference. Typical price (Gas system boiler, like-for-like swap, fitted, hot water cylinder not included), including VAT.
| Region | Typical | vs UK average |
|---|---|---|
| London | £3,800 | +25% |
| South East | £3,500 | +17% |
| South West | £3,300 | +10% |
| East of England | £3,200 | +6% |
| West Midlands | £3,100 | +4% |
| Scotland | £3,100 | +2% |
| East Midlands | £3,000 | UK average |
| Yorkshire and the Humber | £3,000 | UK average |
| North West | £2,900 | −2% |
| North East | £2,900 | −5% |
| Wales | £2,800 | −6% |
| Northern Ireland | £2,600 | −12% |
Common questions about system boilers
What is the difference between a system boiler and a combi?
A combi makes hot water on demand from the mains and has no cylinder. A system boiler heats a cylinder, so it can supply several taps at once and does not depend on mains flow, but it needs room for the cylinder.
Does the price include a new cylinder?
Not in the figure shown. It covers a like-for-like boiler swap where the existing cylinder stays. A new cylinder is a separate line on the quote.
Can I switch from a system boiler to a combi?
Yes, and it is a common change in smaller homes. It takes longer than a swap because the cylinder comes out and the pipework changes, and the cost is higher than a straight swap.
Is VAT charged on a new gas boiler?
Yes. Gas boilers are standard-rated, so the price shown includes VAT. The zero rate for energy-saving materials applies to heat pumps, solar panels and insulation, not to gas boilers.
Where these system boilers prices come from
Guide prices are compiled from published UK price guides, converted to a price before VAT, and shown here with VAT added. They are indicative, not quotations. How we price explains the method.
- greatbritishenergy.com, new boiler cost guide, updated 30 October 2026, quoting Checkatrade fitted prices and Which? brand prices (gas boilers standard-rated at 20%; the page does not say whether its figures include VAT, so they are treated as including it and divided by 1.2)
- energyguide.org.uk, how much to fit a boiler, updated 29 October 2026 (VAT treatment not stated; treated as including VAT and divided by 1.2)
Get quotes for your home
A guide price only takes you so far. Local firms can price the work on your own home, and comparing a few quotes is the quickest way to see what is reasonable.
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