E10
Lux
HVAC Control Relay Drive Fault
Thermostat displays E10 and system will not respond to mode changes
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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
Failed internal relay driver on main PCB, Shorted Y or W output to common, Miswired thermostat terminals
How to Fix / Troubleshooting
Safety: Turn off power to the HVAC system at the breaker before any wiring checks.
- Check for shorts: Remove the thermostat and inspect the Y, W, G, and O/B wires. Ensure no bare copper is touching adjacent terminals or the backplate.
- Isolate thermostat: With power off, disconnect all load wires (Y, W, G, O/B) from the wall plate, leaving only R and C connected. Restore power and see if E10 clears. If it does, the issue is in the wiring or HVAC equipment.
- Reconnect one by one: With power off, reconnect one control wire at a time, restoring power after each to identify which circuit triggers E10.
- Inspect equipment side: For the problematic circuit, inspect the corresponding connection at the furnace or condenser control board for shorts or crushed wires.
- Replace thermostat: If E10 remains even with all control wires removed (only R and C connected), the internal relay driver is likely failed and the thermostat should be replaced.
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Repair Difficulty
Hard
4/5
Required Part
Lux Smart Thermostat Main PCB (relay driver section)
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