The furnace indicates a fan speed error; the fan runs, but its speed feedback is out of range.

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

Defective fan speed sensor, wiring fault between the fan and PCB, incorrect fan calibration, failing fan motor.

Safety: Isolate the power before working on the fan or PCB.

Inspect fan connector: Check the multi-pin plug from the Baxi fan to the PCB for bent pins or corrosion. Reseat it firmly.
Check harness: Look for chafed or pinched wires along the fan harness route.
Observe startup: Restore power and call for heat. Listen for fan ramp-up. If the fan surges or stalls, it may be failing.
Replace fan if needed: If the wiring is sound and the error persists, the fan assembly (with an integrated speed sensor) usually needs replacement.

Hard 4/5

Modulating Combustion Fan

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