E5
Amazon Smart Thermostat
Call for Heat/Cool Output Fault
Thermostat displays E5 and heating or cooling will not start
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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 W or Y output to C or ground, Damaged relay on thermostat main board, Miswired heat pump reversing valve (O/B) terminal
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system at the breaker before working on thermostat wiring.
- Inspect thermostat wiring: Remove the thermostat from the wall plate. Check that W (heat), Y (cool), and O/B (reversing valve, if used) wires are not frayed or touching each other or the C terminal.
- Check at furnace/air handler: Verify that the W and Y wires are correctly landed on the control board and not pinched or shorted to metal.
- Test without load: With power off, disconnect W and Y at the furnace control board. Restore power and see if E5 clears. If it does, the issue is in the field wiring or equipment. If E5 remains, the thermostat output circuit may be faulty.
- Verify heat pump wiring: If you have a heat pump, confirm the O/B wire is on the correct terminal and configured properly in the Alexa app (O or B type).
If E5 persists with all load wires removed, replace the thermostat as its internal relay or triac is likely damaged.
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Repair Difficulty
Hard
4/5
Required Part
Amazon Smart Thermostat Main Control Assembly
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