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Lennox · Heat pump

E433 Inverter compressor over-current (inverter code 29)

High severity

What the control is telling you

Compressor peak phase current above 28 A (six-minute delay at startup). The inverter first slows down (code 14); if current stays high the unit stops. Five times in 60 minutes = lockout. The outdoor control can also trigger 433 if speed falls below minimum at startup. Inverter LED flash code 29 (red 2 flashes, green 9 flashes). S30/S40 thermostat alert code 433 (shown as E433 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 or pressure
  • Older outdoor control software

Test and repair steps

  1. If 433 occurs without inverter flash code 29, the outdoor control triggered it: check its software version in the thermostat outdoor unit diagnostics.
  2. Software 1.27 and later adds a 6-minute (cooling) and 11-minute (heating) delay; update over the internet with auto update on, or replace the outdoor control with catalog 17D27 or newer.
  3. Check for high pressure conditions.
  4. Clear by disconnecting power to both indoor and outdoor units, reconnect and restart.
  5. Check inverter LEDs flash code 29 = red 2 flashes, green 9 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.38. 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.