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Lennox · Furnace

E409 LSOM - low secondary voltage

High severity EL296UHVLennox SL280UHVLennox SL297NV

What the control is telling you

Secondary voltage below 18 VAC; operation stops after 10 minutes.

Applies to: EL296UHV(X) series furnaces with integrated control 103130-XX only

Likely causes

  • Low 24 V supply

Test and repair steps

  1. Measure secondary voltage.
  2. Correct transformer/load issue.
  3. Clears when above 20 VAC for 2 seconds or power reset.

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Source: Lennox EL296UHV(X) Unit Information / Service Literature, Table 5 Ignition Control 103130-XX Diagnostic Codes, p.38. 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.