Why it matters
Condensing boilers are most efficient when the water returning to them is cool enough for them to condense and recover extra heat. If the flow temperature is set very high, the return water stays hot and the boiler condenses less.
Turning it down
On many combi boilers, the heating flow temperature can be lowered on the boiler controls – often to around 60°C or a little below – while hot water for taps stays separate. Rooms may take longer to warm up, and you may need to run the heating slightly longer.
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When to be careful
Lowering flow temperature isn't right for every system:
- Homes with a hot water cylinder need stored water kept hot enough to be safe
- Rooms with undersized radiators may not get warm enough
- Older non-condensing boilers won't benefit in the same way
- Some vulnerable households need rooms to warm up quickly
