Thermostat display shows F0 and heating system does not respond to temperature changes.

Safety first: Turn off power to the thermostat and boiler at the main breaker before removing the thermostat from the wall plate. Risk of electric shock and damage to control electronics.

• Step 1 – Power cycle the system:
  • Switch off the boiler and thermostat circuit breaker for 2–3 minutes.
  • Turn power back on and wait for the thermostat to reboot fully (up to 2 minutes).
  • Check if F0 clears.
• Step 2 – Verify sensor configuration:
  • Enter the installer/advanced menu (refer to Protherm thermostat manual for key combination, typically holding Menu + OK for several seconds).
  • Locate the Sensor Type or Input Configuration setting.
  • Confirm that the correct sensor type is selected (e.g. NTC 10k for Protherm remote room sensor, or Internal if no external sensor is used).
  • Save settings and exit the menu.
• Step 3 – Reset to factory defaults (if misconfigured):
  • In the installer menu, choose Factory Reset or Restore Defaults.
  • Confirm the reset and allow the thermostat to restart.
  • Reconfigure date, time, and schedules.
• Step 4 – If F0 persists:
  • The internal configuration memory or microcontroller may be damaged.
  • Contact a Protherm service center or replace the thermostat main control module.