F.23 is displayed, the boiler cycles off quickly, and the flow temperature rises much faster than the return.
Safety Warning
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
How to Fix / Troubleshooting
Safety: Isolate the power and allow the system to cool before opening any components.
Steps:
- Ensure all radiator valves and any motorized zone valves are open and operating.
- Bleed radiators and the boiler's air vent to remove trapped air.
- Check system pressure and top up if low.
- Listen to the pump: if it is noisy, grinding, or very hot, it may be partially blocked or failing.
- Clean the system filter (if fitted on the return line) to remove sludge and debris.
Advanced: If F.23 persists, the plate heat exchanger or main heat exchanger may be restricted and require chemical cleaning or replacement, and the pump may need replacement. These tasks should be performed by a qualified technician.
Repair Difficulty
Required Part
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