Radiators not heating after a power cut or boiler reset
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Most likely cause & what to check
After a power cut, several components in a central heating system can lose their settings simultaneously — the programmer loses its schedule, some boilers lock out and need resetting, and smart thermostats may lose connection.
Check the boiler display: after a power cut, some boilers show a fault code (e.g., E9, F0, or simply a flashing LED). Press and hold the reset button for 3–5 seconds to restart the boiler. It should ignite and run normally.
Check the programmer or thermostat: the clock may have reset to 00:00 and all programmed schedules will be lost. Reprogram the current time and your heating on/off times. On a Hive or Nest system, the app should reconnect automatically once broadband is restored — check the app status.
Check the thermostat temperature is set above current room temperature. Some thermostats reset to a lower default after a power interruption.
If zone valves or motorised valves have lost their position after the power cut, run the heating in manual override for 30 minutes to allow them to recalibrate. On Honeywell/Drayton systems, valves return to their fail-safe position on power loss (usually closed for heating zone valves).
If the boiler will not reset and shows a persistent fault code, consult our boiler fault codes database with your boiler brand and code for specific guidance, or call a Gas Safe engineer.
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