HVACopedia

Lennox · Heat pump

E345 Relay O failure

High severity

What the control is telling you

O relay fault on a component: the pilot relay coil was not energized or its contacts stayed open. S30/S40 alert code 345; unit control shows E345.

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

Likely causes

  • Failed O relay on the control

Test and repair steps

  1. Check for 24 VAC on O during a heat pump heat call.
  2. Replace the component control.
  3. On Lennox variable capacity outdoor units, replace the outdoor control.
  4. Clears after recovery following reset.

Settings for these units

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.25. 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.