E227 Low pressure switch opened during ignition or run

What the control is telling you

Low pressure switch opened during trial for ignition or while running.

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

Likely causes

• Vent/intake restriction
• Wind or ice at termination
• Inducer problem
• Water in hoses or header box

Test and repair steps

1. Warning: Never jumper or bypass the combustion air pressure switch; it is a safety shutdown device and is not field adjustable.
2. Know the sequence on a heat call the pressure switches must be open; the low-fire switch must close within 120 s of the inducer starting or the inducer goes to high speed; if low and high switches are not closed within 30 s after that, the inducer shuts off for a 5-minute wait. For second stage, the high-fire switch must close within 10 s or a 5-minute delay follows; after 5 failed attempts the furnace runs low fire for the rest of the call.
3. Check the vent (exhaust) and combustion air intake piping for blockage, ice, sags holding water, or bad terminations. After snow, ice or freezing fog, check intake and exhaust terminations and remove any obstruction.
4. Confirm the combustion air inducer starts and runs correctly on both low and high speed; listen for bearing noise.
5. Inspect the pressure switch hoses for cracks, kinks, water, or loose fittings, and confirm they are on the correct ports.
6. Check the condensate trap and the condensate hose screens at the cold end header box for blockage (power off; twist and pull screens, rinse); prime the trap with 10 fl. oz. (300 ml) of water if dry. If furnace and coil drains are combined, the A/C drain must be vented or the pressure switch will not work properly.
7. Measure the switch differential with a manometer: tee into the positive and negative sides at the switch, read at start-up and again after about 5 minutes of steady run.
8. Compare readings to the set-point tables at 0-4500 ft the low/high fire break points are e.g. -045: 0.35/0.60 in. w.c., -090: 0.50/0.90, -110 and -135: 0.45/0.90. Close (make) is 0.15 in. w.c. above the break point.
9. Check pressure switch wiring and connections at the integrated control; replace the switch if the measured differential is adequate but the contacts do not respond.

Settings for these units

Recommended filter size by cabinet width · EL296UHV

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

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

• E223 Low pressure switch failed open
• E224 Low pressure switch failed closed
• E225 High pressure switch failed open
• E226 High pressure switch failed closed
• E228 Inducer calibration failure
• E229 Ignition on high fire
• E240 Low flame current (run mode)
• E241 Flame sensed out of sequence - flame present