Fondital Heating Demand / Diverter Valve Fault

Boiler does not respond to heating demand, but hot water works normally

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

Stuck diverter valve on Fondital combi boiler, Faulty room thermostat or wiring, Diverter motor failure, PCB not receiving heating demand signal

How to Fix / Troubleshooting

Safety: Turn off power before touching any control wiring.

User checks:

Thermostat settings: Ensure the room thermostat is calling for heat and set above room temperature.
Programmer: Check that the heating program is active and not in OFF or holiday mode.
Boiler mode: Confirm the Fondital boiler is not set to DHW-only mode.

Technician actions:

Test the room thermostat and wiring to the boiler.
Check operation of the diverter valve motor and replace if stuck or seized.
Inspect the diverter valve cartridge for debris and replace if worn.
Verify the main PCB is correctly processing heating demand.

Repair Difficulty

Medium 3/5

Required Part

Diverter Valve Assembly

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