Safety first: Turn OFF power. Allow the tank to cool before removing insulation or sensors.

Steps to check:

1. Identify tank sensors: Many hybrids use upper and lower tank sensors. Locate both and verify they are properly inserted into their wells.
2. Check part numbers: Confirm that replacement sensors (if any) match Reliance’s specified part numbers for your model. Mixing different sensor types can cause F8.
3. Inspect wiring: Check each sensor harness for damage and ensure connectors are fully seated at the control board.
4. Compare resistances: With power OFF, disconnect both sensors and measure resistance. At a stable tank temperature, readings should be similar. A large difference indicates a bad sensor.
5. Replace faulty sensor(s): Install new matching tank sensors as needed. If F8 persists with known-good sensors, the control board may require replacement.

Note: Do not interchange upper and lower sensors unless the service manual allows it.

Reliance hybrid water heater displays F8 and may not heat efficiently

Possible Causes