E20
Wyze
O/B Reversing Valve Circuit Fault
Thermostat displays E20 and reports a heat pump O/B reversing valve wiring issue; system may heat when cooling is requested or vice versa.
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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
O/B wire not connected or loose at Wyze base, O/B wire disconnected at air handler or heat pump control board, Incorrect O/B setting (energize in heat vs cool) in Wyze app, Open O/B conductor in thermostat cable
How to Fix / Troubleshooting
Safety first: Turn off power to both the air handler and outdoor heat pump at the breaker.
- Verify system type: Confirm your system is a heat pump and uses an O/B reversing valve terminal.
- Inspect O/B at thermostat: Remove the Wyze display and ensure the O/B wire is fully seated in the O/B terminal.
- Check O/B at equipment: At the air handler or heat pump control board, confirm the same colored wire is attached to the O/B terminal.
- Check Wyze configuration: In the Wyze app, verify whether the reversing valve should be energized in cool or heat based on your equipment manufacturer’s specification. Set this correctly.
- Continuity test: With power off and O/B disconnected at both ends, test continuity of the O/B conductor. Replace the cable if open.
- Restore power and test: Reconnect wiring, restore power, and test both heating and cooling modes to ensure the system operates correctly and E20 clears.
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Repair Difficulty
Medium
3/5
Required Part
Thermostat Cable (O/B Conductor)
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