Thermostat shows E07 and frequently reboots or loses power

Safety first: Isolate mains power to the boiler and any external transformer before working on wiring. Only work on low-voltage terminals if you are competent to do so.

• Verify supply type: Check the thermostat installation manual to confirm whether it should be powered from the boiler's low-voltage terminals or an external transformer. Ensure it is not accidentally connected to 230V.
• Inspect connections: Remove the thermostat from the wall plate and check that the power terminals are tight and the conductors are fully inserted.
• Check cable length and size: Very long or thin cables can cause voltage drop. If the thermostat is far from the boiler, consider using a thicker cable or relocating the thermostat.
• Measure voltage: If you have a multimeter and are competent, measure the voltage at the thermostat power terminals. Compare with the specified range in the manual. If voltage is unstable or low, investigate the boiler's low-voltage output or transformer.
• If supply is stable but E07 persists: The thermostat's internal power circuitry may be faulty. Replace the thermostat.