Boiler shows F23 and stops, often with large difference between flow and return temperatures

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Blocked or partially blocked heat exchanger, Pump running too slow or failing, Closed radiator valves or zone valves, Sludge in system

Safety first: Turn off power and allow the boiler to cool before touching pipework.

Steps to check:

Ensure all radiator valves and any motorised valves are open.
Check system pressure and top up if low.
Bleed radiators to remove air.
Verify that the pump is running and not excessively noisy.
If F23 persists, a system flush and inspection of the primary heat exchanger by a professional is recommended.

Warning: Persistent differential faults indicate circulation problems that can lead to overheating.

Hard 4/5

Circulation Pump

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