Combi vs system vs regular boilers
The three main boiler types explained simply, with the pros and cons of each and how to choose the right one for your home.
Choosing a new boiler starts with picking the right type. There are three main kinds, and the best one depends on your home, your hot water habits and how many bathrooms you have.
Combi boilers
A combi, or combination boiler, heats water on demand directly from the mains. There is no separate tank or cylinder, so it is compact and efficient.
Best for: smaller homes and flats with one bathroom.
- Hot water instantly, no waiting for a tank to heat
- Compact, fits in a kitchen cupboard, frees up loft and airing space
- Efficient, you only heat the water you use
- Can struggle if several taps or showers run at the same time
System boilers
A system boiler works with a hot water cylinder that stores heated water, so multiple taps and showers can run at once with steady pressure.
Best for: homes with two or more bathrooms.
- Strong hot water to several outlets at the same time
- Most parts are built in, making installation tidy
- Needs space for a cylinder, usually in an airing cupboard
- Hot water is limited to the cylinder size, then needs to reheat
Regular boilers
A regular, or conventional, boiler uses both a hot water cylinder and a cold water tank in the loft. They are common in older homes with traditional heating systems.
Best for: larger older homes, or where the existing pipework suits it.
- Good for homes with high hot water demand and older radiators
- Works well with low mains pressure
- Takes up the most space, with a tank and a cylinder
- More components than a combi or system boiler
How to choose
Think about how many bathrooms you have and how often several are used at once. One bathroom usually points to a combi. Two or more points to a system boiler. If you are not sure, our engineers will recommend the right type and size for your home and give you a fixed price.
Frequently asked questions
What is the difference between a combi and a system boiler?+
A combi heats water on demand straight from the mains, with no tank or cylinder needed. A system boiler works with a hot water cylinder, storing hot water so several taps can run at once. Combis suit smaller homes, system boilers suit homes with more than one bathroom.
Which boiler type is best for a large house?+
Homes with two or more bathrooms usually do best with a system or regular boiler and a hot water cylinder, so several outlets can run at once without losing pressure. A large combi can work but may struggle if several showers run together.
Can I switch from one boiler type to another?+
Yes. Many homeowners switch from a regular boiler to a combi to free up space and remove tanks. It costs more than a like-for-like swap because of extra pipework, but it can be well worth it. An engineer will advise what suits your home.
Related guides
ComparisonBest combi boiler for a small house or flat
The best combi boilers for smaller homes and flats, where a compact, efficient, well-priced boiler beats a big powerful one.
AdviceBoiler Pressure Too High? How to Bring It Down
If your pressure gauge is sitting in the red, here's how to safely bring your boiler pressure back down without calling an engineer.
AdviceBoiler Leaking Water: Causes and What to Do
A puddle under your boiler is never normal. Here's what causes leaks, what to do right now, and when it's time for a repair or replacement.
Need a boiler replacement?
Tell us about your boiler and we will get you a fixed price. No obligation.