while frequently cited for the D1NA series

As a genuine Johnson Controls replacement part

the internal bimetal disc in the switch may have fatigued

It features two setpoint windows

This switch is designed to trip (open) at 160°F and automatically reset (close) once the temperature drops by 30°F

Williams P500406 Limit Switch while frequently cited for theThe Williams P500406 Limit Switch is a critical safety component designed for precise thermal regulation in Williams Monterey top vent heaters and furnace gas valves. Engineered with a 270 degree Fahrenheit Cut Out, this Manual Reset (M R) limit switch serves as a reliable failsafe, interrupting the electrical circuit to the gas valve if internal temperatures exceed safe operating parameters. This specific HVAC high limit control is essential for