E224 Low pressure switch failed closed

What the control is telling you

Low-fire pressure switch stays closed on a heat call for longer than 150 seconds.

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

Likely causes

• Switch contacts stuck closed
• Jumpered switch
• Wiring short

Test and repair steps

1. Check whether the low pressure switch is stuck closed at the start of a heat call (more than 150 seconds).
2. The control checks that the pressure switches are open before the inducer starts; a switch closed at that point blocks ignition.
3. Warning: Remove any jumper across the pressure switch; it must never be bypassed.
4. Check the switch wiring for a short.
5. Measure operating pressure with a manometer and compare to set-point tables.
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. Inspect vent and inducer operation.
8. Replace the switch if contacts are stuck.

Settings for these units

• Recommended filter size by cabinet width · EL296UHV
• Recommended filter size by cabinet width · Lennox SL280UHV
• Filter sizes by cabinet width · Lennox ML180UHE
• Filter sizes by cabinet width · Lennox SL297NV