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.
What the fix costs
A switch that cannot open is mechanically simple to price — the repair guide's $150–400 pressure switch band — but E224 carries two cheaper possibilities a good visit checks first. A shorted run of wire in the switch circuit reads closed to the control just as convincingly as welded contacts, and repairs as wiring for far less than a switch. And moisture bridging the switch or its connector — a real hazard on a condensing furnace with a sluggish drain — clears with the drainage problem for close to nothing. The discipline that keeps this repair honest: whatever is found must explain a switch that reads closed with the inducer off, before any airflow exists. A quote blaming the vent or the inducer for this particular code has misread it; those affect whether the switch closes, not whether it can open. More codes like this across brands: pressure switch codes.
DIY or call a pro
There is nothing outdoors to clear for this one — E224 is detected before the inducer ever spins, so terminations and drafts are not the story — and that removes the usual homeowner checklist entirely. What remains is the integrity of a safety interlock, which is the least appropriate DIY territory in the furnace: the control has found the vent-proving check disabled and has correctly refused to start, and the only good outcome is a technician determining whether contacts, wiring, moisture or a leftover jumper disabled it. That last item is the piece of history you may hold — if the furnace was serviced recently, particularly for a pressure switch complaint, say so directly, because a jumper installed as a “temporary” fix and forgotten produces exactly this code, and its removal must come with an answer to why it was ever there. Do not power-cycle hunting for a lucky start; the furnace is not confused, it is protecting you.
What this looks like
From the outside, this usually shows up as the inducer spins up but the burners never fire — that walkthrough covers what to check in order, and when it stops being a homeowner job.