HVACopediaLennox · Furnace
Power-up size code Unit size code shown at power-up (variable speed)
What the display is showing
When 24 V power comes up, the display briefly shows the stored unit size code, a character that stands for the furnace model and capacity. If instead three horizontal bars appear and then a steady E203 follows, the control does not recognise a size code and must be programmed.
Applies to: Lennox SL280UHV, SL280UHNV and SL297UHNV variable speed furnaces
What to do
- To confirm a programmed size, cycle 24 V power and read the code on the display.
- If three bars show, redo the program unit size (P) procedure.
Settings for these units
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
| Cabinet | Side return | Bottom return |
|---|---|---|
| 17-1/2 in. (040, 060) | 16 x 25 x 1 (1) | 16 x 25 x 1 (1) |
| 21 in. (080) | 16 x 25 x 1 (1) | 20 x 25 x 1 (1) |
No filter or rack supplied; use a field high-velocity rated filter and keep one in place whenever the unit runs.
Models that show this code
14 models in Lennox SL280UHV, Lennox SL280UHNV, Lennox SL297NV
Other codes on the same units
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Source: Lennox SL297UHNV Installation 507760-02 (02-2018), Program Unit Capacity/Size Mode, printed p.60-61; SL280UHV 508245-01 p.56-57; SL280UHNV 1601-L8 Program Unit Capacity/Size Mode. Summarized in our own words; check the original manual for your model.
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.