HVACopediaLennox · Furnace
E380 EIM interlock relay fault
What the control is telling you
EIM interlock relay energized but its input not sensed after three seconds (furnace or air handler modes); no heating or cooling. S30/S40 thermostat alert code 380 (shown as E380 on the unit control display).
Applies to: Lennox communicating gas furnaces (e.g. SL280UHV/SL280UHNV, EL296UHV) in S30/S40 smart thermostat systems
Likely causes
- Failed interlock relay on the EIM
- Wiring fault
Test and repair steps
- Check EIM interlock wiring.
- The EIM drops the relay, waits five minutes, and tries again if the call is still there.
- Replace the EIM if the relay fails.
- Clears after the fault recovers.
Settings for these units
- Recommended filter size by cabinet width · EL296UHV
- Recommended filter size by cabinet width · Lennox SL280UHV
- Filter sizes by cabinet width · Lennox ML180UHE
- Filter sizes (filter rack kits) · Lennox EL195UHNE
- Filter sizes by cabinet width · Lennox SL297NV
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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.28. Summarized in our own words; check the original manual for your model.
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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.