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Lennox · Furnace

542 Zone 1 temperature sensor fault

Medium severity

What the control is telling you

Zone 1 sensor reading out of range or open/short for more than five seconds; zone shows '--', system runs central mode (all dampers open). Escalates after 10 minutes. Thermostat shows 'Problem (Zoning Control)'. S30/S40 thermostat alert code 542.

Applies to: Lennox communicating gas furnaces (e.g. SL280UHV/SL280UHNV, EL296UHV) in S30/S40 smart thermostat systems

Likely causes

  • Loose or miswired sensor connections
  • Open or shorted sensor
  • Two sensors assigned the same zone number

Test and repair steps

  1. Check sensor and damper control module terminals for loose or incorrect wiring.
  2. Check zone number assignments; no two sensors may share a number.
  3. Replace the sensor if open or shorted.
  4. Clears 30 seconds after the condition ends.

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Source: Lennox Residential Communicating Systems Alert Code Guide (V2) 100017 (3/2023), Table 2 Alert Codes and Troubleshooting, p.45. 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.