F20
Ideal
DHW Demand Recognition Fault
Display shows F20, heater may not respond to hot water demand but heating may still work (on combi-type water heater systems).
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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.
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Possible Causes
Faulty microswitch on diverter valve, Stuck diverter valve, Broken DHW demand wiring, Faulty flow switch
How to Fix / Troubleshooting
Safety: Turn off power and water supply before opening hydraulic components.
- Check hot water flow: Confirm strong flow at taps. If flow is weak, address plumbing restrictions first.
- Inspect diverter valve (if fitted): Look for leaks or signs of sticking. Lightly tap the valve body with a non-metallic tool to free a stuck mechanism (temporary only).
- Check DHW microswitch: Ensure the microswitch actuator moves when a hot tap is opened. If not, the valve may be seized.
- Professional service: Diverter valves and microswitches are service parts; have them replaced if F20 persists.
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Repair Difficulty
Hard
4/5
Required Part
Diverter Valve Microswitch
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