Boiler shows A20, heating demand present but burner does not start, 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 power and allow boiler to cool before working on hydraulic components.

Steps:

Listen for the diverter valve motor when switching between heating and 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 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

Check Price on Amazon

We may earn a commission from links on this page.