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Lennox · Air handler

501 PureAir UV sensor fault

Medium severity

What the control is telling you

UV sensor shows a fault or stays silent over 5 minutes, so UV lamp life can't be worked out (reads '-'). S30/S40 alert code 501.

Applies to: Lennox communicating air handlers and EIM-equipped indoor units in S30/S40 smart thermostat systems

Likely causes

  • PureAir S accessory issue

Test and repair steps

  1. Check UV sensor wiring.
  2. Replace the sensor if it does not recover.
  3. Clears 30 seconds after recovery.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.44. 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.