HVACopedia

Lennox · Furnace

E250 Limit switch circuit open

High severity EL296UHVLennox SL280UHVLennox ML180UHELennox SL297NV

What the control is telling you

Primary limit is open; control runs the blower and closes the gas valve. If the limit does not reclose within 3 minutes the unit goes into a 1-hour soft lockout.

Applies to: EL296UHV(X) series furnaces (integrated control 103130-XX and 107045-XX)

Likely causes

  • Overfiring
  • Low airflow (dirty filter, closed registers, blower problem)
  • Blocked heat exchanger

Test and repair steps

  1. Inspect the filter (should be checked monthly) and replace if dirty; oversized pressure drop from high-efficiency filters can trip the limit.
  2. Measure external static pressure heating speed must not exceed 0.8 in. w.c.
  3. Measure temperature rise (supply minus return) and confirm it is within the rating-plate range, adjusting blower heat speed (DIP 11-13) if needed.
  4. Check gas pressures with a manometer supply natural gas 4.5-13.0 in. w.c. (LP 11.0-13.0); manifold natural 1.7 low fire / 3.5 high fire (LP 4.5 / 10.0) at 0-4500 ft. Clock the gas meter to confirm input; if manifold pressure is right but rate is wrong, check orifices.
  5. Check the blower wheel for debris and verify blower operation.
  6. Check for blockage in the heat exchanger.
  7. The limit must reclose within 3 minutes or the control enters Watchguard for 1 hour; do not substitute a limit with a different set point.

Settings for these units

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.

Open the app

Source: Lennox EL296UHV(X) Unit Information / Service Literature, Table 5 Ignition Control 103130-XX Diagnostic Codes, p.35; Ignition Control 107045-XX Diagnostic Codes table, p.42, Troubleshooting: Heating Sequence of Operation flowchart, p.110-112, Typical Operating Characteristics p.86, Maintenance p.86-87, Heating System Service Checks p.82-85. 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.