IVT Runaway heating / thermostat control failure

Furnace runs continuously and overheats the house

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

Thermostat contacts stuck closed, Miswired thermostat, Shorted thermostat cable, Control board relay stuck

Safety: Turn off power to stop heating if the furnace will not shut off.

Check thermostat: Set the thermostat to OFF. If the furnace continues to run, the issue is likely in wiring or the control board.
Inspect wiring: Remove the thermostat and separate the call-for-heat wire (often W) from the terminal. If the furnace stops, the thermostat or cable is faulty.
Test at furnace: At the IVT control, disconnect the thermostat input. If the furnace still runs, the control relay may be stuck and the board needs replacement.

Medium 3/5

IVT room thermostat

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