If the control board signals a "stuck open" fault

ensuring the B1809904S ignition control remains stable under variable line voltage conditions

eliminating the need for auxiliary relays in many setups

the Intermatic ET2715C is the direct performance successor

6 1/2" Length

Lochinvar & A.O. Smith 100109846 Limit Switch 322838-753 If the control board signalsThe Lochinvar & A. O. Smith 100109846 is a 90 150F M R limit switch engineered for high precision thermal protection in residential and commercial water heating systems. As a critical safety component, this manual reset thermostat monitors air or water temperature to prevent overheating conditions that can lead to equipment failure or hazardous operation. It is specifically designed for cross brand compatibility, serving as a direct replacement part