Thermostat shows F1 and does not display room temperature; heating may run continuously or not at all.

Safety warning: Always isolate power at the breaker before opening the thermostat housing. Do not touch live terminals.

• Step 1 – Reboot the thermostat:
  • Turn off power to the thermostat/boiler for 2 minutes.
  • Restore power and check if F1 clears.
• Step 2 – Check installation location:
  • Ensure the thermostat is not installed above a radiator, in direct sunlight, or near a heat source that could overheat the internal sensor.
  • Move curtains or furniture that may trap heat around the thermostat.
• Step 3 – Inspect for physical damage:
  • Remove the thermostat from the wall plate.
  • Check the front housing and PCB for signs of liquid ingress, burn marks, or cracks.
  • If there is visible damage, the internal sensor is likely irreparable.
• Step 4 – Switch to external sensor (temporary workaround):
  • If your Protherm model supports an external room sensor, connect a compatible Protherm NTC room sensor to the sensor terminals.
  • In the installer menu, change the sensor source from Internal to External.
  • Confirm that the thermostat now reads a valid temperature.
• Step 5 – Replace thermostat if needed:
  • If no external sensor is available or F1 persists, replace the thermostat or its main PCB assembly.