E8
Rheem
Outdoor Unit Communication Loss
Thermostat shows E8 and may indicate 'Outdoor unit communication error' or 'No response from condenser/heat pump'.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Open or shorted communication cable to outdoor unit, Outdoor unit control board not powered, Tripped outdoor disconnect or breaker, Failed outdoor control board communication circuit
How to Fix / Troubleshooting
Safety first: Turn off power at the outdoor disconnect and indoor breaker before opening any panels.
Steps:
- Check outdoor power: Verify the outdoor disconnect is on and the breaker is not tripped. Restore power if off.
- Inspect communication wiring: Open the outdoor unit control panel and confirm the ABCD (or designated) communication terminals match the indoor unit and thermostat. Look for loose or corroded connections.
- Check cable condition: Inspect the cable jacket for UV damage, rodent chewing, or cuts. Repair or replace damaged sections.
- Board status LEDs: Observe the outdoor control board LEDs and compare to the Rheem service label. A dead board or error pattern may indicate board failure.
- Test continuity: With power off, ohm the communication conductors between indoor and outdoor units to confirm no opens or shorts.
- If E8 persists with proper wiring and power: The outdoor control board communication circuit may be defective and should be replaced by a qualified technician.
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Repair Difficulty
Hard
4/5
Required Part
Outdoor Unit Control Board
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