HVACopediaLennox · Air handler
E371 Float switch sensed open
What the control is telling you
The air handler float switch is open; after 10 minutes (600 s) the alert escalates from service soon to service urgent. S30/S40 thermostat alert code 371 (shown as E371 on the unit control display).
Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems
Likely causes
- Plugged condensate drain or trap
- Float switch tripped or faulty
Test and repair steps
- Clear the condensate drain and trap and empty the pan.
- Check the float switch and its wiring.
- Clears after the fault recovers.
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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.