Lennox furnace E224: Pressure switch failed closed
E224 means the pressure switch was found closed when it should have been open — before the inducer started. A switch that is always closed cannot prove anything, so the furnace refuses to run.
Applies to: Lennox gas furnaces with a seven-segment diagnostic display on the control board, such as the ML193UHEK, per installation instructions 508565-01.
What it means
With the inducer off there is no suction, so a working pressure switch must sit open. Finding it closed tells the control the switch is stuck, shorted, or bypassed, and therefore useless as a safety interlock — it would read closed whether the flue were clear or completely blocked. This is why the furnace stops rather than continuing: the check that proves the vent is clear has been disabled, not merely failed. Lennox's troubleshooting is the same set of measurements as for E223, because the same pressures and the same vent conditions are involved, but the conclusion is usually different. A switch that will not close points outward at the vent; a switch that will not open points at the switch and its wiring.
Most common causes
- A failed pressure switch with stuck or welded contacts.
- A short in the pressure switch wiring, which is electrically identical to a closed switch.
- A switch jumpered during earlier service and never restored.
- A pressure switch of the wrong specification fitted in a previous repair.
- In rare cases a vent or wind condition holding the diaphragm over with the inducer off.
How to diagnose it
- Note whether the furnace has been serviced recently. A jumper left across a pressure switch is a real and dangerous cause.
- Note whether the inducer starts at all — on this fault the control should stop before it does.
- There is nothing here a homeowner can safely check inside the cabinet.
How to fix it
- Technician work. This concerns the interlock that proves the flue is clear.
- Expect the wiring to be checked for a short before the switch is condemned.
- If a jumper is found, it must come out, and the reason it was fitted has to be found.
- A replacement switch must match the specification for the model, not merely fit the fitting.
Notes
On the communicating alert code list the nearest equivalent is 226, high pressure switch stuck closed. The numbers do not match between the two Lennox systems, which is why the model and the display type matter.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.