Thermostat shows E4 and will not control the load; often appears on electric underfloor heating models

Safety first: Turn off power to the heating circuit immediately at the breaker to prevent floor damage or fire risk.

Steps to troubleshoot:

• Allow the floor and thermostat to cool down for at least 30–60 minutes.
• Check thermostat settings: verify maximum floor temperature and safety limits in the Tuya app or on the device menu; reset to manufacturer defaults if unsure.
• Inspect the floor sensor wiring at the thermostat for correct connection and no shorts to the heating cable.
• Measure floor sensor resistance and compare to the temperature chart; if it reads much lower than expected (indicating falsely high temperature), replace the sensor.
• With power restored briefly, listen for the thermostat relay clicking on/off. If the relay remains stuck ON even when the thermostat is off, the relay contacts are welded and the thermostat must be replaced.
• After replacing the faulty sensor or thermostat, re-enable power and monitor operation to ensure the E4 code does not reappear.

Warning: Persistent E4 errors with actual floor overheating require inspection of the heating mat/cable by a qualified electrician.