Display shows E3 and thermostat cannot regulate temperature correctly

Safety first: Turn OFF power at the breaker before removing the thermostat from the wall.

Steps to troubleshoot:

• 1. Power cycle the thermostat:
  • Turn off the breaker for 1–2 minutes.
  • Turn it back on and check if E3 persists. Temporary glitches can clear with a power reset.
• 2. Inspect for moisture and damage:
  • Remove the thermostat front and inspect the electronics for signs of condensation, corrosion, or physical cracks.
  • If the thermostat is installed in a bathroom or humid area, ensure adequate ventilation and that the back box is not filled with moist air.
• 3. Switch to floor sensor control (if available):
  • On models like Heatit Z-TRM3, enter the installer menu and set control mode to Floor sensor only or Floor + Room depending on your installation.
  • This can temporarily bypass a faulty internal room sensor.
• 4. Factory reset:
  • Perform a factory reset according to the user manual to rule out configuration errors.
• 5. Replace thermostat front module if fault remains:
  • If E3 persists, the internal sensor on the PCB is likely defective.
  • Replace the Heatit thermostat front module (or entire thermostat) with a compatible model.