Boiler displays A20; heating demand is present, but the burner does not start. The 3-way valve may move.

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

Stuck diverter valve, Faulty diverter motor/actuator, Position microswitch failure, Debris in valve body

Safety: Isolate the power supply and allow the boiler to cool before working on hydraulic components.

Steps:

Listen for the diverter valve motor when switching between heating and domestic hot water. No sound may indicate motor failure.
A technician should remove the diverter motor head and check that the valve spindle moves freely; free it or replace if seized.
Test the position microswitches or feedback potentiometer and replace the actuator if faulty.
If the valve body is blocked with debris, flush or replace the diverter valve assembly.

Hard 4/5

3-Way Diverter Valve Assembly

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