Combi vs system boiler: which is right for you?
The right boiler type depends on your home's size, hot-water demand and space. Here's how to choose.
When replacing a boiler, one of the first decisions is the type. For most UK homes it comes down to combi versus system. Here's the plain difference.
Combi boilers
A combi heats water on demand, straight from the mains — no tank, no cylinder. Compact and efficient, ideal for smaller homes and flats with one bathroom.
- No tank or cylinder — saves space.
- Hot water on demand.
- Generally cheaper to install.
- Can struggle if several taps/showers run at once.
System boilers
A system boiler works with a hot-water cylinder, storing hot water ready for use. Better for larger homes with multiple bathrooms and higher simultaneous demand.
- Handles multiple bathrooms well.
- Steady pressure even with several taps running.
- Needs space for a cylinder.
- Stored hot water can run out and needs reheating.
The quick rule
One bathroom, limited space → usually a combi. Multiple bathrooms, higher demand → often a system boiler. We'll confirm the best fit at survey.
What about heat-only (conventional) boilers?
There's a third type worth knowing: the conventional or "heat-only" boiler, which works with both a hot water cylinder and a cold water tank (usually in the loft). These are common in older homes. When replacing one, many people switch to a combi to free up space, or to a system boiler to keep stored hot water without the loft tank — we'll advise which makes sense for your home.
The quick decision guide
- Small home, one bathroom, limited space → combi.
- Larger home, multiple bathrooms, high demand → system.
- Replacing an old conventional system → we'll help you choose.