HomeGuidesCombi or system boiler
Combi or system boiler: which does your house need?
The short answer, the fitted prices, and the two questions that settle it.
Read this if
Your boiler is due for replacing and you have been told you need a different type, or you are not sure the one you have still suits the house.
Price a new boilerThe guide
Which type suits which house
The short answer: a combi boiler suits most homes with one bathroom, and a system boiler suits homes with two or more bathrooms used at the same time. A combi heats water the moment you turn a tap on, so there is no cylinder and no waiting, but it can only feed so much hot water at once. A system boiler heats a cylinder of stored water, so two showers can run together.
Fitted, a combi typically costs £1,800 – £2,800, a system boiler £2,400 – £3,400 and a regular boiler £2,200 – £3,200, including VAT. The spread within each range is mostly the make and output of the boiler, the size of the house, and whether the flue or pipework has to move.
Two questions decide it. First, how many hot taps and showers does your household run at once? If the answer is regularly more than one, a combi will struggle. Second, what is your mains water pressure and flow? A combi can only deliver what the mains gives it, so a weak supply means a weak shower. Andy measures the flow at the survey.
Switching type costs more than a like-for-like swap. Going from a regular boiler with loft tanks to a combi means taking out the tanks and cylinder and reworking pipework; going from a combi to a system boiler means finding room for a cylinder. Both are common, and both are priced at the survey rather than guessed.
A regular (heat-only) boiler is mainly worth keeping where the house is plumbed around it, or where the mains supply is too weak for a combi. And if a heat pump is on the cards in the next few years, bear in mind that it needs a hot water cylinder too, which counts in favour of a system setup now.
Side by side
The three types compared
Typical fitted prices in Morley and Leeds, including VAT. Your written price comes after a survey.
| Boiler type | Typical fitted price | How it works and who it suits |
|---|---|---|
| Combi | £1,800 – £2,800 | Heats water on demand. No cylinder, no loft tanks. Best for flats and homes with one bathroom. |
| System | £2,400 – £3,400 | Heats a hot water cylinder; no loft tanks. Best for two or more bathrooms used at once. |
| Regular (heat-only) | £2,200 – £3,200 | Cylinder plus cold water tanks in the loft. Keep it where the house is plumbed around it. |
Questions
Common questions
Is a combi boiler cheaper to run than a system boiler?
Not by much, and it depends on the house. A combi avoids keeping a cylinder of water hot, which saves a little heat. A system boiler with good controls can be just as efficient. Choose on how your household uses hot water, not on running cost.
Can a combi boiler run two showers at once?
It can try, but the flow is shared, so both showers get weaker. A bigger combi helps a little. If two showers at once is a daily event in your house, a system boiler with a cylinder is the better fit.
Do I have to change boiler type when I replace mine?
No. Most people replace like for like, which is the cheapest option. Changing type is worth it when the old setup no longer suits the household, such as a combi in a house that now has two bathrooms.
Not sure which you need?
Andy checks your hot water use and mains flow at a free survey, then gives you a fixed price for the right boiler.