HVACopediaLennox · Air handler
E345 Relay O failure
What the control is telling you
O relay fault on a component: the pilot relay coil was not energized or its contacts stayed open. S30/S40 alert code 345; unit control shows E345.
Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems
Likely causes
- Failed O relay on the control
Test and repair steps
- Check for 24 VAC on O during a heat pump heat call.
- Replace the component control.
- On Lennox variable capacity outdoor units, replace the outdoor control.
- Clears after recovery following reset.
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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.25. Summarized in our own words; check the original manual for your model.
Homeowner looking at this code? See what it means for you and when to call a technician.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.