Lennox furnace E223: Pressure switch failed open
E223 means the pressure switch did not close when it should have. The inducer is running but the control never got the signal that proves the flue is clear, so it will not light the burners.
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
The pressure switch is a diaphragm switch connected by a small hose to the inducer housing. Suction from a running inducer pulls it closed, and that closure is the proof the control needs before it will energise the igniter and open the gas valve. A switch that stays open means either the suction is not there or the switch cannot respond to it. Lennox's troubleshooting is unusually concrete: check the pressure in inches of water column at which the switch closes on a heat call, measure the actual operating pressure, and inspect the vent and combustion air inducer for correct operation and restriction. That turns a parts-swap into a measurement — the switch either sees the pressure it needs or it does not, and the number says which.
Most common causes
- A blocked vent or intake termination outside — snow, ice, a nest, or a cap left in place.
- Water in the pressure switch hose, the collector box, or a blocked condensate drain.
- A cracked, kinked or disconnected hose.
- An inducer running but not developing enough suction, from worn bearings or a dirty wheel.
- A failed pressure switch, or one of the wrong specification fitted previously.
How to diagnose it
- Check the vent and intake terminations outside. This is homeowner work and it resolves a large share of these in cold weather.
- Note whether the inducer sounds normal, weak or noisy.
- Note any standing water near the furnace, which points at the condensate path.
- Everything inside the cabinet is technician work.
How to fix it
- Clear the vent or intake termination if it is blocked.
- Otherwise this is a technician job, and Lennox's own steps are measurements rather than replacements.
- Never jumper the pressure switch to force the furnace to fire. That interlock is what stops it burning gas when the flue is not clear.
Notes
E223 and E224 are the two halves of the same switch. Failed open means it never closed; failed closed means it was already closed before the inducer started, so it could not prove anything.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
What the fix costs
Lennox's two-measurement method — the pressure at which the switch closes versus the operating pressure the inducer actually produces — is also the honest pricing method, because the gap between those numbers is what you are really buying. Plenty of margin with a switch that will not close: switch work, at the repair guide's $150–400, with its check-the-flue-first caveat. Operating pressure barely above (or below) the setpoint: the money belongs on the draft side — restriction cleared cheaply, or an inducer at $300–900 — and a new switch would fail the same way next week. That second scenario is the one where homeowners routinely pay twice, once for the switch that didn't fix it and again for the inducer that did. Ask which of the two numbers was out of spec; a diagnosis that can't answer hasn't measured either.
DIY or call a pro
Before anyone bills you, walk the intake and exhaust outside and check that the condensate path is moving — the no-tools checks that clear a meaningful share of these codes, especially in snow, leaf-fall or hard-freeze weather. Past that line the diagnosis is manometer work by definition: E223's entire troubleshooting method is comparing pressures in inches of water column on a live heat call, and no visual inspection substitutes for it. The switch itself is the interlock that keeps gas shut until the flue proves it can carry combustion products, so the standing rule holds absolutely — never jumper it, even briefly, even to confirm a suspicion. One behavior note that costs nothing: this code resumes normal operation once the fault clears, so a furnace that heals itself on a windless morning has not been fixed; log that it happened and in what weather.
The same fault on other brands
Among E-code peers specifically, Trane's E32 reports the same never-closed condition on its S9V2 controls, Carrier's code 31 is the long-standing equivalent, and ICP's 3 flashes covers Heil, Tempstar and Comfortmaker furnaces. The pressure switch hub maps all 47 relatives; what distinguishes Lennox's version is spelling out the closing-pressure-versus-operating-pressure comparison in the code table itself.
What this looks like
From the outside, this usually shows up as the furnace starts and stops in short bursts — that walkthrough covers what to check in order, and when it stops being a homeowner job.