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Lennox · Furnace

LED1 ON / LED2 SLOW flash Rollout switch open

Critical severity Lennox G43UF

What the control is telling you

The flame rollout switch has tripped. The 12-pin plug not seated on the board gives the same signal.

Applies to: G43UF-24B-045 through G43UF-60D-135 (SureLight boards 32M88, 78M47, 100973-01)

Likely causes

  • Burners overfiring above nameplate input (manifold pressure or orifice size wrong)
  • Orifices leaking at the manifold
  • Air leaks in the heat exchanger or sooted or restricted heat exchanger
  • Burners not centered in the burner box
  • Rollout switch failed or miswired
  • 12-pin connector not fully seated or bad pin

Test and repair steps

  1. Turn off power at the disconnect before touching wiring or components. Gas work: qualified gas tech only.
  2. Push the top button to reset the rollout switch, but find the cause before leaving the furnace.
  3. Check continuity across the switch after resetting. Replace it if it has no continuity.
  4. Check switch wiring and the 12-pin connector at the board.
  5. Check manifold pressure and orifice size against the nameplate, and check the input rate.
  6. Check the orifices for leaks with an approved leak detection method.
  7. Check the heat exchanger for air leaks and sooting, and check burner position.

Settings for these units

Models that show this code

10 models in Lennox G43UF

G43UF-24B-045G43UF-24B-070G43UF-36B-070G43UF-36C-090G43UF-36C-090HG43UF-48C-090G43UF-48C-110G43UF-48C-110HG43UF-60C-110G43UF-60D-135

Other codes on the same units

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Source: Lennox G43UF Unit Information Corp. 0416-L4, Troubleshooting Chart Problems 1.2 and 5.3 pp.50, 54 and Table 4 p.11. 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.