The three types at a glance
| Combi | System | Regular (heat-only) | |
|---|---|---|---|
| Hot water cylinder | No | Yes | Yes |
| Loft tanks | No | No | Yes |
| Hot water | On demand, from the mains | Stored, at mains pressure | Stored, usually gravity-fed |
| Best for | Flats and homes with 1 bathroom | Homes with 2+ bathrooms | Older homes, low mains pressure |
| Space needed | Least | Airing cupboard | Airing cupboard and loft |
Combi boilers
A combination boiler heats water directly from the mains as soon as you turn on a tap, and provides your central heating from the same compact unit. There is no hot water cylinder and no tanks in the loft.
- Hot water on demand — you never run out
- Frees up the airing cupboard and loft space
- Usually the quickest and most affordable to install
- Flow rate is shared, so running two showers at once can be weak
- Performance depends on your mains water pressure and flow
System boilers
A system boiler heats water that is stored in an unvented hot water cylinder, usually in an airing cupboard. The main components, such as the pump and expansion vessel, are built into the boiler, so there are no loft tanks.
- Several taps and showers can run at the same time
- Good for larger homes and families
- Works well alongside solar thermal panels and heat pumps
- Needs space for a cylinder, and the stored hot water can run out
- Unvented cylinders need an annual safety check
Regular (heat-only) boilers
Regular boilers — also called conventional or heat-only boilers — are found in many older Essex homes. They work with a hot water cylinder and a cold water storage tank, plus a small feed and expansion tank in the loft.
- Ideal where the existing pipework or radiators would not cope with mains pressure
- Suits areas with low mains water pressure
- Lets you keep an immersion heater as a hot water backup
- Uses the most space and gravity-fed showers can be weak without a pump
Which one is right for my home?
As a rule of thumb, a combi suits most flats and houses with one bathroom. If you have two or more bathrooms used at the same time, a system boiler with an unvented cylinder usually gives a better experience. A regular boiler is often the sensible like-for-like replacement where the house already has tanks and older pipework.
Before recommending a boiler, our engineers check your mains water pressure and flow rate, the number of bathrooms, and your existing pipework. Book a free survey through our boiler installation page.