HVACopediaLennox · Furnace
E252 Discharge air temperature too high
What the control is telling you
Discharge air temperature is too high during gas heat.
Applies to: EL296UHV(X) series furnaces (integrated control 103130-XX and 107045-XX)
Likely causes
- Low airflow
- Overfiring
Test and repair steps
- Inspect the filter (should be checked monthly) and replace if dirty; oversized pressure drop from high-efficiency filters can trip the limit.
- Measure external static pressure heating speed must not exceed 0.8 in. w.c.
- Measure temperature rise (supply minus return) and confirm it is within the rating-plate range, adjusting blower heat speed (DIP 11-13) if needed.
- 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.
- Code clears when the heat call ends.
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 SL297NV
Models that show this code
22 models in EL296UHV, Lennox SL280UHV, Lennox SL297NV
Other codes on the same units
- E229 Ignition on high fire
- E240 Low flame current (run mode)
- E241 Flame sensed out of sequence - flame present
- E250 Limit switch circuit open
- E270 Soft lockout - no flame after max retries
- E271 Soft lockout - retries exceeded, pressure switch opened
- E272 Soft lockout - recycles exceeded, pressure switch opened
- E273 Soft lockout - recycles exceeded, flame failure
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.
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, Typical Operating Characteristics p.86, 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.