Buderus Fan Stuck in Continuous Mode or Stuck Relay

Furnace fan runs continuously even when there is no call for heat

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

Fan set to ON at thermostat, Stuck fan relay on Buderus control board, Incorrect wiring causing constant fan signal

Safety: Turn off power before accessing control wiring.

Steps:

Thermostat setting: Ensure the fan mode on the thermostat or Buderus room controller is set to AUTO, not ON.
Reset control: Power-cycle the furnace to see if the fan stops after reboot.
Check wiring: Inspect low-voltage wiring between thermostat and furnace for shorts between fan and power terminals.

If the fan continues to run with correct settings and wiring, the fan relay on the control board may be stuck and the board will need replacement.

Medium 3/5

Buderus Control Board (Main PCB)

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