HVACopediaLennox · Air handler
502 PureAir UV lamp off
What the control is telling you
The last three light intensity readings were below threshold. S30/S40 thermostat alert code 502.
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
- Check lamp power and replace the UV lamp if failed.
- Clears when a set of five samples is above threshold.
Save it for the next call
Star this code in the HVACopedia app and keep the whole library on your phone for jobs with no signal.
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.