The /U suffix simply denotes "Universal" or retail packaging

Always verify the schematic on the unit's access panel to ensure the R621 designation matches your specific application

C and 1371

meaning it is calibrated to trip and interrupt the burner circuit when flue temperatures reach 225 degrees Fahrenheit

an HVAC flame sensor with a cracked ceramic insulator or significant pitting on the rod should always be replaced to ensure long-term reliability and safety

Honeywell T87K1007 Thermostat The /U suffix simply denotesThe Honeywell T87K1007 is a mercury free, digital round thermostat designed for precision control in 2 wire heat only systems. Operating within a standard 18 30Vac range, this unit utilizes battery assisted power stealing to ensure consistent performance without requiring a common wire, making it a reliable solution for retrofitting older heating systems. The internal thermistor sensor element provides exceptional 1 degree accuracy, maintaining tight