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Lennox · Heat pump

E440 Inverter compressor slowdown - high heat-sink temperature (inverter code 13)

Low severity

What the control is telling you

Heat sink near its limit; the compressor slows (about 4 Hz, 5-6%) to cool it. Speed reduction starts above 185 F and full speed resumes at 176 F. Normal for 3-4 minutes above 110 F outdoor (dealer information). Inverter LED flash code 13 (red 1 flash, green 3 flashes). S30/S40 thermostat alert code 440 (shown as E440 on the unit control display).

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

Likely causes

  • High outdoor temperature
  • Debris on heat sink
  • Loose heat sink screws

Test and repair steps

  1. If frequent, especially at lower outdoor temperatures, check the heat sink (back of inverter, in condenser airstream) for debris or blocked airflow.
  2. Warning: Wait five minutes for capacitors to discharge, then tighten the heat sink screws.
  3. Heat sink temperature, compressor Hz and speed reduction status are in the outdoor unit diagnostics.
  4. Clears automatically.
  5. Check inverter LEDs flash code 13 = red 1 flash, green 3 flashes. Normal inverter LEDs with no fault: red ON, green OFF.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.42. 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.