Quick answer: A combi suits most flats and homes with one bathroom. A system boiler suits homes with two or more bathrooms. A heat only boiler suits older homes with a cylinder and loft tanks, or homes with low mains water pressure.
There are three main types of gas boiler. The right one depends on how many bathrooms you have, your water pressure and how your heating is set up now.
At a glance
| Combi | System | Heat only | |
|---|---|---|---|
| How it heats water | Straight from the mains when you turn on a tap | Heats a hot water cylinder | Heats a hot water cylinder fed by loft tanks |
| Hot water cylinder | Not needed | Needed | Needed |
| Loft tanks | Not needed | Not needed | Needed |
| Several taps at once | Can struggle | Yes | Yes |
| Best for | Flats and homes with one bathroom | Homes with two or more bathrooms | Older homes, low mains pressure, or keeping your existing setup |
Combi boilers
A combi heats your radiators and gives you hot water straight from the mains whenever you turn on a tap. There is no hot water cylinder or loft tanks, so you get cupboard and loft space back and never run out of hot water. The trade-off is that a combi shares its power between taps, so it suits homes where one shower or tap is usually running at a time.
System boilers
A system boiler heats your radiators and a hot water cylinder, usually kept in an airing cupboard. There are no loft tanks, and because the hot water is stored, several taps and showers can run at once. That makes a system boiler the usual choice for homes with two or more bathrooms.
Heat only boilers
Heat only boilers are also called regular or conventional boilers. They work with a hot water cylinder and tanks in the loft, so they suit traditional heating systems. They are a good choice for older homes, homes with low mains water pressure, or if you want to keep your existing setup and avoid extra work.
Which boiler type should you choose?
- Choose a combi if you live in a flat or a home with one bathroom and want to free up space.
- Choose a system boiler if you have two or more bathrooms or often run more than one shower at a time.
- Choose a heat only boiler if you have a traditional system with loft tanks, low mains pressure, or want the simplest like-for-like swap.
Once you know the type, compare the brands: Worcester Bosch, Vaillant, Ideal, Viessmann, Baxi and ATAG.
Frequently asked questions
Can I switch from a heat only boiler to a combi?
Usually, yes. Switching means removing the cylinder and loft tanks, so it takes a little longer to fit, but you get the space back. We check your water pressure and flow first to make sure a combi will work well in your home.
Is a combi or system boiler better for two bathrooms?
For two or more bathrooms, a system boiler is usually better because stored hot water lets more than one shower run at once. A powerful combi can work in some homes, and we will advise when we survey.
Which boiler type is cheapest to run?
Running costs depend more on the boiler’s efficiency and how your home is insulated than on the type. A combi only heats the water you use, which can save energy in smaller homes, while a system boiler can work better with solar or heat pump upgrades later on.
Get the right boiler for your home
Tell us a little about your home and we will recommend the right type, size and model, then give you a clear quote. Browse all the boilers we install or get a boiler quote.
