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Lennox · Heat pump

E438 Inverter PFC input over-current (inverter code 73)

High severity

What the control is telling you

PFC over-current detected; inverter resets after three minutes. 10 times in a rolling 60 minutes = lockout. Inverter LED flash code 73 (red 7 flashes, green 3 flashes). S30/S40 thermostat alert code 438 (shown as E438 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 load
  • High pressure
  • Outdoor fan failure

Test and repair steps

  1. Look at the thermostat and outdoor control for other alert codes or high pressure trips.
  2. Check outdoor fan operation.
  3. Service urgent clears when the inverter is power cycled.
  4. Check inverter LEDs flash code 73 = red 7 flashes, 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.41. 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.