Watkins Flow Switch 34874

The flow switch is located in the heater interlock relay coil circuit. When the switch is closed (proper flow), voltage is transferred to the heater interlock coil when the control thermostat calls for heat. Activating the relay allows the heater to activate. When the switch is open (low flow), voltage to the heater interlock relay coil is interrupted regardless of the state of the control thermostat. This prevents the heater from activating until the low flow condition has been resolved.