Boiler displays F10, may start then shut down, temperature readings unstable

Safety: Turn off power and gas. Allow the boiler and system to cool before bleeding or opening any components.

System checks:

• Check system pressure and top up to the recommended level if low. Bleed radiators and the boiler’s air vent to remove trapped air.
• Ensure all radiator valves and isolation valves near the boiler are fully open.
• Clean any system filters or strainers (e.g., magnetic filter, Y‑strainer) that may be restricting flow.

Boiler checks:

• Verify that the circulation pump runs during a heating demand. If it is noisy, hot, or not spinning, it may be partially seized and should be replaced.
• If the pump is OK but ΔT remains high, the primary heat exchanger may be internally blocked with sludge or scale. A qualified technician should perform a chemical clean or replace the heat exchanger.

After repair: Reset the boiler and monitor flow and return temperatures via the diagnostic menu to confirm that the temperature difference is within Protherm’s specified range and F10 does not recur.