The furnace shows a flow switch or flow sensor fault (on systems with flow detection); the burner will not fire for heating.

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 flow switch, blocked flow sensor turbine, airlock in the primary circuit, faulty flow sensor wiring.

Safety: Turn off the power and allow the system to cool.

Bleed system: Remove air from high points and radiators to ensure good circulation.
Check pump: Confirm that the Baxi circulation pump is running and that all valves are open.
Inspect flow sensor: On models with a flow turbine, remove it and check for debris or sludge. Clean gently and refit with new seals if required.
Test switch: For mechanical flow switches, verify that the paddle moves freely and that the microswitch operates when flow is present.

Medium 3/5

Primary Flow Sensor / Flow Switch

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