What should I do if my combi boiler has hot water but no heating?

Can I ignore this problem?

Because your hot water still works, it’s easy to assume this isn’t a serious problem — but that assumption is exactly what causes costly boiler failures. When your combi boiler has hot water but no heating, it usually means heat isn’t circulating properly. Valves stick, pumps strain, and components overheat quietly in the background. Each day you leave it unchecked, internal parts are pushed harder, energy is wasted, and the risk of total heating failure increases — often right when temperatures drop. The smart move is simple: act early. A Gas Safe engineer can diagnose the issue, restore proper heat flow, and fix the fault before it escalates into a far bigger (and far more expensive) problem.

Main possible causes

• Stuck or faulty diverter valve – this valve directs heat to either radiators or taps. If it gets stuck in hot water mode, radiators stay cold.

• Pump failure / seized circulation pump – boiler heats water, but it doesn’t get pushed to radiators.

• Airlocks in pipes / radiators – pockets of air block circulation.

• Low system pressure – often affects heating before hot water.

Steps you can try

1. Check boiler pressure (aim ~1–1.5 bar).
2. Bleed radiators to release trapped air.
3. Check thermostat and heating controls (ensure heating is actually switched on).
4. Engineer call-out if problem persists — most of these faults require professional parts replacement.