Honeywell Electronic board SM07402U

The Honeywell SM07402U is an electronic control board (PCB) designed for use in Honeywell wall-hung boilers. It manages the ignition and safety sequence, including fan pre-purge, airflow confirmation, ignition transformer activation, gas valve operation, and flame detection via an ionization electrode. The board also reads temperature sensors and modulates fan speed and gas valve position to control boiler output. This board is compatible with Honeywell SM07402U and SM07402 models.

Parts of this type are selected by matching the original part number or manufacturer code printed on the board. The replacement must match the exact series designation, supply voltage, safety times (pre-purge and safety time), and flame detection method. The physical connection pattern, including pin layout or plug shape, must be mechanically and electrically compatible with the existing wiring harness. Always verify the boiler's serial number range or production date, as hardware revisions may occur without changing the model designation.

When control boards of this type fail, the boiler may not start or may lockout due to flame detection issues. Symptoms include the fan not running, no ignition spark, or the gas valve not opening. Check for error codes on the boiler display, verify power supply to the board, and inspect the board for visible damage such as burnt components or blown fuses.