When a unit is run in bypass mode for long periods of time, the water temperature in the pump heats up, which can ultimately cause damage. A thermal relief valve judges the temperature in the pump, and dumps this hot water while bringing in cold water, preventing damage to the pump.
Specifications
Part #: 85.300.042
Part #: 85.300.101
Part #: 85.300.102
Part #: 85.300.104
Part #: FBV-33