Your boiler has detected that the water temperature in your underfloor heating circuit is outside of the expected safe range, causing the system to stop working.

Under-floor system temperature fault

What causes this fault?

This fault occurs when the water temperature entering your underfloor heating loops exceeds a safe threshold, triggered by a safety thermostat. The most common reasons are a failure in the external mixing valve that regulates heat or a pump failure that prevents hot water from moving through the system quickly enough. It is designed to prevent excessive heat from warping floorboards or damaging sensitive pipework.