HVACopedia

Lennox · Heat pump

E404 Compressor rotor locked

High severity

What the control is telling you

The compressor rotor is locked up. S30/S40 thermostat alert code 404 (shown as E404 on the unit control display).

Applies to: Lennox communicating heat pumps incl. variable-capacity inverter units in S30/S40 smart thermostat systems

Likely causes

  • Shorted run capacitor
  • Seized bearings
  • Excessive liquid refrigerant in compressor

Test and repair steps

  1. Check the run capacitor.
  2. Check for liquid floodback / overcharge.
  3. A hard start kit may be needed.
  4. Clears after four consecutive normal run cycles or power reset.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.29. 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.