HVACopediaLennox · Furnace
E240 Low flame current (run mode)
What the control is telling you
Flame signal is weak while running.
Applies to: EL296UHV(X) series furnaces (integrated control 103130-XX and 107045-XX)
Likely causes
- Dirty or oxidized flame sensor
- Poor unit ground
- Burner/flame not contacting sensor
Test and repair steps
- Enter Flame Signal mode hold the diagnostic push button until a solid F shows, release, and read flame current in microamps.
- Compare 2.6 uA or more is normal, 2.5 uA or less is low, and the flame drops out at 1.1 uA.
- Warning: Turn off power and gas before removing the flame sensor from the left side of the burner support.
- Clean the sensor rod (remove oxide) or replace it if damaged or still weak after cleaning.
- Measure neutral-to-ground voltage and verify the furnace has a solid earth ground; the control is polarity sensitive.
- Check ground at the control AC volts between line neutral and the C terminal should not exceed 2 VAC at idle, 5 VAC with inducer/ignitor on, 10 VAC with blower on; a wide swing under load means a poor ground. Line hot to neutral should be 97-132 VAC.
- 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.
- Clean burners if dirty (soft brush vacuum on burner faces) and confirm burners are centered in the burner ports.
- Run a heat cycle and confirm stable flame current.
Settings for these units
Recommended filter size by cabinet width · EL296UHV
| Cabinet width | Side return | Bottom return |
|---|---|---|
| 17-1/2 in. | 16 x 25 x 1 in. (1) | 16 x 25 x 1 in. (1) |
| 21 in. | 16 x 25 x 1 in. (1) | 20 x 25 x 1 in. (1) |
| 24-1/2 in. | 16 x 25 x 1 in. (2) | 24 x 25 x 1 in. (1) |
Number in brackets is the quantity of filters.
Filters are field supplied and installed outside the furnace; inspect monthly.
Recommended filter size by cabinet width · Lennox SL280UHV
| Cabinet width | Side return | Bottom return |
|---|---|---|
| 14-1/2 in. | 16 x 25 x 1 in. (1) | 14 x 25 x 1 in. (1) |
| 17-1/2 in. | 16 x 25 x 1 in. (1) | 16 x 25 x 1 in. (1) |
| 21 in. | 16 x 25 x 1 in. (1) | 20 x 25 x 1 in. (1) |
| 24-1/2 in. | 16 x 25 x 1 in. (2) | 24 x 25 x 1 in. (1) |
Number in brackets is filter quantity; filters are field supplied.
Never run the unit without a filter installed.
- Filter sizes by cabinet width · Lennox ML180UHE
- Filter sizes by cabinet width · Lennox SL297NV
Models that show this code
34 models in EL296UHV, Lennox SL280UHV, Lennox ML180UHE, Lennox SL297NV
Other codes on the same units
- E226 High pressure switch failed closed
- E227 Low pressure switch opened during ignition or run
- E228 Inducer calibration failure
- E229 Ignition on high fire
- E241 Flame sensed out of sequence - flame present
- E250 Limit switch circuit open
- E252 Discharge air temperature too high
- E270 Soft lockout - no flame after max retries
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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, Heating System Service Checks p.82-85, Maintenance p.88-89, Unit Components p.52. 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.