IVT Control Stuck On / Relay Fault

Boiler runs continuously and overheats the house even when thermostat is turned down

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 relay on external wiring center, Shorted thermostat cable, PCB relay stuck closed, Diverter valve stuck in heating position

Safety: You can temporarily turn off the boiler at the isolator to stop heating.

Steps:

Check that the room thermostat is not set too high and is not located near a heat source.
If using a wireless thermostat, ensure it is communicating correctly with the receiver.
A technician should test the call-for-heat terminals at the boiler to see if they remain live when they should be off.
Inspect external wiring centers and relays for stuck contacts.
If the boiler PCB relay is stuck, replace the main control PCB.

Medium 3/5

Main Control PCB

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