Safety first: Turn OFF power at the breaker. Avoid bending or damaging refrigerant lines while working near the coil.

Steps to check:

1. Access evaporator area: Remove the top cover to expose the evaporator coil and fan assembly. Locate the evaporator temperature sensor clipped to the coil.
2. Inspect sensor and clip: Ensure the sensor is firmly attached to the coil surface. Reattach or reposition if it has fallen off.
3. Check wiring: Follow the sensor harness to the control board. Look for chafed insulation, pinched wires, or corroded connectors. Reseat the plug.
4. Measure resistance: With power OFF and sensor disconnected, measure resistance and compare to Reliance’s thermistor chart. Replace the sensor if readings are out of spec.
5. Reassemble and test: After replacing or reseating the sensor, reinstall the cover, restore power, and test heat pump operation.

Note: Persistent F2 after sensor replacement may indicate a control board fault.

Reliance hybrid water heater displays F2 and heat pump mode is disabled

Possible Causes