Safety: Isolate electrical power and close the gas valve before opening the casing.

Clean the flame sensor: Remove the ionisation probe from the burner assembly. Gently clean the metal rod with fine abrasive pad to remove oxidation. Refit ensuring it is correctly positioned in the flame.
Check grounding: Verify that the burner and chassis earth connections are tight and free of corrosion. A poor earth can prevent the PCB from sensing flame.
Inspect cables: Check the ignition/flame sensing lead from the electrode to the Baxi control PCB for damage, burns, or loose connectors. Reseat connectors firmly.
Test operation: Restore power and gas, reset the unit, and observe ignition. If the burner still shuts down after a few seconds, the PCB flame detection circuit may be faulty.

Professional help: Replacement of the main control PCB or gas valve should be done by a qualified Baxi service technician.

Furnace locks out shortly after ignition, burner lights briefly then shuts down

Possible Causes