Tap your way around the inside of a boiler to see what every part does — and the warning signs that it needs attention — then find the system type your home uses.
These are the components our engineers check at every service. Tap a numbered point on the diagram — or a label beside it — to see what each part does and the warning signs it gives when something's wrong.
Every gas-heated home uses one of these three setups. Pick the one closest to yours, then tap a numbered point on the diagram to see what each part does.
Flats and small-to-medium homes with one bathroom and good mains water pressure. No tanks or cylinder means it saves space and gives unlimited hot water on demand — but running two showers at once will split the flow between them.
Homes with two or more bathrooms, where several taps or showers may run at the same time. The hot water cylinder stores plenty in advance, and there's no loft tank to worry about — you just need an airing cupboard or similar space for the cylinder.
Older and larger properties that already have tank-based pipework, and homes with lower mains water pressure — the loft tanks feed the system by gravity. Often the simplest like-for-like replacement if your home already has one, keeping disruption and cost down.
You (or a schedule) set a target temperature, and the thermostat signals the system to start.
The gas valve opens, the burner fires, and the heat exchanger transfers the flame's heat into the water.
A pump pushes hot water out through the flow pipe to every radiator and back again.
Each radiator warms the room; TRVs let you control individual rooms independently.
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