Burner starts ignition sequence but locks out with no flame signal after a few seconds

Safety: Disconnect power to the furnace and close the fuel shutoff valve before opening the burner housing.

Inspection steps:

• Clean ionization electrode: Remove the ionization electrode from the burner head. Gently clean the rod with fine abrasive pad to remove soot and oxidation. Do not bend the rod. Reinstall with the correct insertion depth and distance to the burner head as per Weishaupt specifications.
• Check UV sensor (if equipped): For burners using a UV flame detector, remove the sensor and clean the viewing window with a lint-free cloth. Ensure the sensor is correctly aimed at the flame zone and that the mounting is tight.
• Inspect wiring: Trace the flame sensor cable from the sensor back to the burner control (W-FM/WCM). Look for cuts, crushed insulation, or loose terminals. Reseat all plug connectors.
• Check grounding: Ensure the burner chassis and control module are properly grounded. A poor ground can prevent correct flame rectification.
• Control reset: Restore power and fuel, then reset the burner once. Observe whether flame is established and stays on. If lockout persists, the control module or sensor may be defective.

Note: Flame signal strength and control module integrity should be checked by a qualified technician with appropriate test instruments.