Thermostat does not power on at all (no display, no response)

Safety first: You will be working near mains voltage. Turn off the breaker before removing the thermostat. Only measure live voltage if you are trained and have proper tools.

Steps to troubleshoot no‑power condition:

• 1. Check breaker and switches:
  • Verify the relevant circuit breaker is ON and any local isolation switches are not off.
• 2. Inspect wiring at thermostat:
  • Turn off the breaker.
  • Remove the Fibaro thermostat from the wall plate.
  • Confirm that live (L) and neutral (N) wires are present and firmly connected.
• 3. Measure supply voltage:
  • With power restored and using a multimeter, measure between L and N at the thermostat.
  • If there is no voltage, the issue is upstream (wiring, junction box, or breaker).
• 4. Check for signs of damage:
  • If correct voltage is present but the thermostat remains dead, inspect the PCB for burn marks or a burnt smell.
• 5. Replace thermostat if internal supply is faulty:
  • If supply voltage is correct and wiring is good, the internal power supply is likely failed and the thermostat should be replaced.

When to call a professional: If you are not comfortable measuring mains voltage or tracing circuits, contact a licensed electrician.