Thermostat shows E6 and does not respond to setpoint changes

Safety first: Turn off power at the main breaker. Confirm power is off before touching any wiring.

Steps to troubleshoot E6 (relay fault):

• 1. Verify load rating:
  • Check the heating load (e.g., underfloor heating mat, electric radiator) power rating in watts.
  • Compare with the Fibaro thermostat's maximum load rating printed on the back (e.g., 3A/16A depending on model).
  • If the load exceeds the rating, the relay may have been damaged.
• 2. Listen for relay click:
  • Restore power briefly and change the setpoint from low to high.
  • Listen for a distinct click from the thermostat. No click may indicate a failed relay or control circuit.
• 3. Inspect PCB:
  • With power off, remove the thermostat and inspect the relay area for burn marks or discoloration.
• 4. Test output voltage:
  • With power on and a call for heat, measure voltage at the output terminals using a multimeter (only if you are trained and comfortable working with live mains).
  • If there is no output despite a heat demand, the relay is likely faulty.
• 5. Replace thermostat or use contactor:
  • If the relay is defective, replace the thermostat module.
  • For high loads, install an external contactor or relay module controlled by the Fibaro thermostat's output to protect the internal relay.

When to call a professional: Relay and mains voltage diagnostics should be performed by a qualified electrician. If you suspect overloading or wiring issues, do not continue using the thermostat until inspected.