E11
Lux
O/B Reversing Valve Output Fault
Thermostat displays E11 and heat pump reversing valve will not energize correctly
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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
Shorted O/B terminal to common, Failed O/B relay on thermostat, Incorrect heat pump configuration (O vs B setting)
How to Fix / Troubleshooting
Safety: Turn off HVAC power at the breaker.
- Verify configuration: In the Lux thermostat installer settings, confirm whether the heat pump uses O (energize in cooling) or B (energize in heating) and set accordingly.
- Inspect O/B wiring: Remove the thermostat and check the O/B wire for nicks or shorts to other conductors or the backplate.
- Continuity check: With power off, disconnect the O/B wire at both thermostat and air handler ends and test continuity to ensure the conductor is not shorted to other wires.
- Test without load: Reconnect R and C only, leaving O/B disconnected. Restore power and see if E11 clears. If it does, the problem is in the wiring or reversing valve coil.
- Check reversing valve coil: At the outdoor unit, measure the resistance of the reversing valve coil. Replace the coil if it is shorted or open.
- Replace thermostat: If E11 persists with O/B disconnected, the internal O/B relay is likely defective and the thermostat should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Lux Smart Thermostat O/B Output Circuit
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