Combi or system boiler, which should I get?

It depends on the house and how it gets used. Here’s how to think it through.

The difference

A combi heats water as you use it. Turn on a hot tap and it fires up and heats the water on its way through. No cylinder and no tanks in the loft.

A system boiler heats a cylinder of hot water that’s stored ready to use. When the cylinder’s empty, you wait for it to heat up again.

When a combi suits

• One bathroom, or two that don’t get used at the same time
• You’d like the airing cupboard or loft space back
• You’d rather not heat water you might not use

For a lot of two and three bedroom houses with one bathroom, a combi is the usual choice.

When a system boiler suits

• Two bathrooms used at once. A combi delivers a set amount of hot water per minute, shared between everything running. Two showers at once from one combi can mean two weak showers.
• A full house with everyone getting ready at the same time
• Weak mains water pressure. A combi can only work with what comes into the house. If the incoming supply is weak, a combi will feel weak too.

The thing to check

If you’re being quoted for a combi in a house with more than one bathroom, ask whether the incoming water pressure and flow have been measured. That’s what decides whether a combi will keep up.

If you’re not sure which you’ve got now or which you’d need, put it on the form and we can talk it through when I ring.