Thermostat or underfloor controller shows 'Overheat Protect' or high temperature warning; heating output is disabled.

Safety first: If any part of the system feels excessively hot or smells of burning, switch off the boiler and heating power at the fused spur and call a professional.

• Check location: Ensure the thermostat is not directly above a radiator, on a chimney breast, or in direct sunlight. If it is, relocate it to an internal wall away from heat sources.
• Underfloor systems: If using a floor sensor, verify that the maximum floor temperature limit in the installer menu is set correctly (typically 27–29°C for timber floors).
• Power cycle: Turn the thermostat off and back on, or remove power for 1–2 minutes, then restore. See if the error clears.
• If error persists with normal room temperature: The sensor may be faulty or shorted. A heating engineer should test and replace the sensor or thermostat as required.