E250
Lennox
High Voltage Polarity / Grounding Error
Lennox communicating thermostat displays E250; furnace may not operate or may be locked out.
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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
Line and neutral reversed at furnace power connection, Open or missing equipment ground, Shared neutral issues with other equipment, Incorrect wiring at service disconnect feeding Lennox furnace
How to Fix / Troubleshooting
Danger: This involves 120/240V line voltage. If you are not trained, do not attempt this. Turn off power at the breaker before opening any electrical compartment.
- 1. Verify breaker and disconnect: Confirm the correct breaker is feeding the furnace and that any external disconnect is properly installed.
- 2. Check polarity: At the furnace junction box, verify the hot (usually black) is on the L (line) terminal and neutral (white) is on N. Ground (green/bare) must be securely attached to the furnace chassis.
- 3. Correct miswiring: If hot and neutral are reversed, correct them at the nearest accessible junction or panel according to local electrical code.
- 4. Restore power and reset: After corrections, restore power and allow the thermostat to clear the E250 code.
Because of shock and fire risk, this work is best performed by a licensed electrician or qualified HVAC technician.
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Repair Difficulty
Professional Required
5/5
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