When you replace a boiler, the biggest decision is the type. Choose wrong and you end up with lukewarm showers or a cupboard full of tank you did not need. Here is a plain-English guide to the combi or system boiler question for typical homes in Scotland.
How a combi boiler works
A combi heats water directly from the mains when you turn on a tap. There is no hot water cylinder and no tanks in the loft, so it frees up space. It suits flats and houses with one bathroom, where only one tap or shower runs at a time.
How a system boiler works
A system boiler heats water into a hot water cylinder, usually in an airing cupboard. Because the hot water is stored, two showers can run at once with strong flow. It suits homes with two or more bathrooms and busy households.
Combi or system boiler: quick comparison
| Question | Combi | System |
|---|---|---|
| Bathrooms | 1 | 2 or more |
| Hot water cylinder | No | Yes |
| Two showers at once | Weak | Yes |
| Space needed | Small | Boiler plus cupboard |
| Works with solar or heat pump later | Less easily | Yes |
What about mains water pressure?
A combi is only as good as the water coming into your home. Some older properties and rural homes around Stirling and the Trossachs have low mains flow. We measure it during the survey, because it can decide the answer on its own.
Thinking about a heat pump later?
Heat pumps need a hot water cylinder. If you plan to switch in the next few years, keeping or fitting a cylinder now can save work later.
Still unsure? Try the estimator on our prices page, or book a free survey through our boiler installation page and we will recommend the right type for your home.