E228
Lennox
Low Voltage / Communication Bus Error
Thermostat shows E228; furnace may not run or may run only in limited mode; often associated with low-voltage issues.
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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
Undersized or long thermostat cable causing voltage drop, Loose R and C connections at Lennox board, Failing 24V transformer, Shorted accessory (humidifier, outdoor unit contactor coil) on R-C circuit
How to Fix / Troubleshooting
Safety: Turn off furnace power before inspecting wiring.
- 1. Inspect R and C wiring: Confirm tight, corrosion-free connections at the Lennox control board and thermostat. Re-strip and re-terminate any oxidized or loose wires.
- 2. Disconnect accessories: Temporarily remove wires to external accessories (humidifier, outdoor unit, zone panel) from R and C. Restore power and see if E228 clears. If it does, reconnect accessories one at a time to find the faulty device.
- 3. Check cable length and gauge: For long runs, ensure thermostat wire is at least 18 AWG. Replace undersized cable if necessary.
- 4. Transformer test: A professional can measure 24VAC under load. If voltage sags significantly when the furnace starts, the transformer may need replacement.
Persistent E228 usually requires a technician to evaluate the low-voltage system and transformer.
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Repair Difficulty
Hard
4/5
Required Part
24V Transformer
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