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Lennox · Heat pump

E434 Inverter communication error to main control (inverter code 53)

High severity

What the control is telling you

The outdoor control lost communication with the inverter during a call; compressor demands and the indoor blower stop (blower will not run in test mode until reset). Retries by cycling the contactor off 2 minutes, three times, before lockout. Inverter LED flash code 53 (red 5 flashes, green 3 flashes). S30/S40 thermostat alert code 434 (shown as E434 on the unit control display).

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

Likely causes

  • Outdoor power off while indoor 24 VAC stays on (or the reverse) during service
  • Loose or disconnected connections
  • Interrupted main power to inverter

Test and repair steps

  1. Check for loose or disconnected electrical connections and main power to the inverter.
  2. Reset cycle outdoor unit power off and on, then cycle indoor power (24 VAC to the outdoor control) off and on.
  3. Refer to the unit service manual.
  4. Check inverter LEDs flash code 53 = red 5 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.39. 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.