Combi boilers save space in smaller homes, while system boilers suit larger households.
The real test isn’t the label on the boiler. It’s what happens when somebody turns on a second shower. Here’s how combi, system and regular boilers handle different household routines.
Three things to know.
- Choose a combi for single-bathroom homes to save space
- Select a system boiler if you have multiple bathrooms
- Check your mains water pressure before deciding
Combi boiler
Heats water instantly from the mains — no tank, no cylinder. Ideal for flats and homes with one bathroom. Downside: flow is shared, so running a shower and a kitchen tap together reduces both.
System boiler
Heats a hot water cylinder (usually in an airing cupboard) but doesn't need a tank in the loft. Good for homes with two or more bathrooms where people shower at the same time. You need space for the cylinder and to wait for it to reheat if you use it all.
Regular (heat-only) boiler
The traditional set-up with a cold-water tank in the loft and a vented cylinder. Sometimes kept in older homes where the pipework suits it, or where mains pressure is weak.
Typical matches
As a rough guide:
- Terraced house or flat, one bathroom — combi.
- Three or four-bed semi with an extra shower room — often system.
- Older house with low mains pressure — regular, or improved supply first.
For appliance-specific steps, follow your boiler or product manual. Work inside a gas boiler must be left to a Gas Safe registered engineer.