The most common symptom is short cycling

This SPST (Single Pole Single Throw) controller is specifically designed for unit heaters

For potable water or open heating systems

including models SC8238T402 and SC8238T405

If the status LED shows a specific lockout code related to internal communication or relay failure

Lochinvar & A.O. Smith 100166238 Switch 318820-201 The most common symptom isThe Lochinvar & A. O. Smith 100166238 Gas Pressure Switch is a critical safety component designed for high performance gas fired boilers and commercial water heaters. Featuring a 1 20" WC adjustable range, this manual reset gas pressure switch ensures system integrity by monitoring incoming or manifold gas pressure. If pressures deviate from the calibrated setpoint, the switch initiates a safety lockout, preventing hazardous combustion conditions.