De Dietrich Fan Overrun / Control Fault

Boiler fan runs continuously even when there is no heat demand

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 PCB, incorrect parameter setting, flue gas sensor requiring extended purge, faulty temperature sensor

Safety: Isolate power before inspecting electronics.

Check demand: Ensure no hidden demand from frost protection, anti-legionella cycle, or cylinder reheat.
Power reset: Turn off the boiler for several minutes and restore power to clear a latched relay state.
Technician tasks: A professional should check the main control PCB for a stuck fan relay, verify sensor readings, and adjust parameters if necessary.

Hard 4/5

Main Control PCB

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