Honeywell Electronic control board SM18501

The Honeywell SM18501 is an electronic control board (PCB) designed for use in modern wall-hung boilers. It functions as the burner control, managing the ignition and safety sequence, including pre-purge, airflow confirmation, ignition transformer activation, gas valve opening, and flame proving within the safety time. If no flame is detected, the board initiates lockout. It also reads the flame signal and interacts with temperature sensors and modulating actuators for output control. This board is factory-programmed for a specific boiler model or series and is not interchangeable across different models.

Parts of this type are selected by confirming the exact part number and ensuring the board matches the original unit in the system. Before ordering, verify the board's physical connector pattern and the boiler's model designation, as a mismatched control board will fail to communicate or create a safety hazard. The safety times, pre-purge duration, flame detection method, and input voltage must match the appliance exactly.