Boiler shows F20 and locks out, often with high temperature readings

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 primary circuit, Pump failure, Air in system, Faulty NTC giving incorrect high reading

Safety first: Turn off power and let the boiler cool fully.

Steps to check:

Check system pressure and repressurise if needed.
Bleed radiators and any automatic air vents.
Listen for pump operation; if silent or excessively hot to touch, it may be seized.
Inspect flow and return NTC sensors and wiring for damage.
Reset the boiler. If F20 recurs, a professional should check pump performance and system cleanliness.

Warning: Repeated overheating can damage the heat exchanger and seals. Do not ignore this fault.

Hard 4/5

Circulation Pump

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