For applications requiring a circulator to start on temperature rise

any breach of the tube will render the thermostat non-functional and require a full replacement

While cleaning with a light abrasive can temporarily resolve flame detection issues caused by carbon buildup

leading to erratic damper or valve positioning

For technicians servicing Reznor UDAP

McDonnell & Miller FS4-3 Switch Refrigerant For applications requiring a circulatorFor contractors requiring reliable system protection, the McDonnell & Miller FS4 3 (Part Number 114400) is a heavy duty general purpose liquid flow switch designed to monitor flow in heating, cooling, and water process lines. This 1" NPT unit features a single pole, double throw (SPDT) configuration, allowing you to easily integrate signal lights, alarms, motors, or burners into the control circuit. Engineered to operate at a max pressure of 160 PSI