Siemens Burner control unit LME39.400C2

The Siemens LME39.400C2 is a microprocessor-based burner control unit for gas fan burners. It manages the complete ignition and safety sequence, including pre-purge, flame monitoring, gas valve control, and automatic fuel shut-off in case of faults. The unit is designed for two-stage burners and operates with forced draft air supply. It features a plug-in connection and is housed in impact-proof, heat-resistant, and flame-retarding plastic. The control supports ionization flame detection and is compatible with various flame sensors.

When selecting a replacement burner control of this type, verify the exact series designation and safety time, as mismatched timing profiles create a safety hazard. The physical plug-in base pattern must match the existing socket. Confirm the supply voltage and burner type (gas, forced draft, two-stage). The control is not interchangeable across different series even within the same brand. Ensure the flame detector type (ionization or UV with adapter) is compatible.

Typical failures include lockout due to flame loss, no flame establishment at the end of safety time, or repeated ignition attempts. The equipment may shut down and require manual reset via the lockout button. Check for faulty or soiled fuel valves, flame detector issues, or poor burner adjustment. Also verify air and gas pressure switches and the safety loop.