What is a Combi Boiler?
A combi (combination) boiler is a single unit that provides both central heating and hot water on demand. Unlike older system boilers, there's no separate hot water cylinder or cold water tank — the boiler heats water directly from the mains when you turn on a tap.
How Does a Combi Boiler Work?
When you turn on a hot tap, the boiler detects the flow and fires up to heat the water as it passes through the heat exchanger. When you turn the tap off, the boiler shuts down. This makes combi boilers very efficient — you only heat the water you actually use.
Pros of a Combi Boiler
- Instant hot water (no waiting for a cylinder to heat)
- Compact — no cylinder or tank required
- Energy efficient — heats water on demand
- Lower installation cost than system boilers
Cons of a Combi Boiler
- Can struggle with multiple simultaneous hot water uses
- Not compatible with traditional power showers
- Slightly lower water flow rate than system boilers with a large cylinder
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