Boiler attempts to start but shuts down quickly with E02 displayed

Safety: Turn off power and close the gas valve before opening the burner compartment.

• Clean flame sensor: Remove the flame sensor (or combined igniter/flame rod) from the burner. Gently clean the metal rod with fine steel wool or emery cloth until shiny. Do not sand the ceramic insulator.
• Check mounting and ground: Reinstall the sensor so it is fully in the burner flame path. Ensure the burner assembly and sensor bracket have a solid metal-to-metal contact with the boiler chassis for proper grounding.
• Inspect wiring: Trace the flame sensor wire back to the Dettson control board. Look for damaged insulation, loose spade connectors, or corrosion. Reseat connectors firmly.
• Verify gas pressure (pro only): If the flame is weak or unstable, a licensed technician should measure inlet and manifold gas pressure at the Dettson gas valve and adjust or replace components as required.
• Control board check: If the sensor and wiring are good and flame is strong but E02 remains, the flame rectification circuit on the control board may be faulty. Have a technician test microamp flame signal and replace the Dettson boiler control board if needed.