Lennox furnace E227: Pressure switch opened during ignition or run
E227 means the pressure switch closed normally and then opened again during the trial for ignition or while the furnace was running. The draft was proved and then lost.
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
This is the most informative of the three pressure switch codes, because it says the switch works. It closed. Then, part way through ignition or during the run, it opened again, which means the draft that had been proved went away. That points at something marginal rather than something broken: an inducer that starts strongly and fades, a vent that is partially restricted rather than fully blocked, condensate accumulating during the cycle until it interferes, or a switch operating right at its setpoint so that any small change tips it over. Lennox's troubleshooting is again a measurement — compare the pressure at which the switch closes on a heat call against the actual operating pressure, and inspect the vent and inducer for restriction.
Most common causes
- A partially restricted vent or intake, which allows enough draft to start but not to sustain.
- Condensate building up during the cycle in the collector box, hose or drain.
- An inducer weakening under load, often from bearing wear or a dirty wheel.
- A pressure switch operating marginally, close to its setpoint.
- Wind conditions affecting a vent termination during operation.
How to diagnose it
- Note how far into the cycle the furnace gets before it stops — that timing is genuinely useful to a technician.
- Check the vent and intake terminations outside for partial obstruction, not only complete blockage.
- Note whether the fault is worse in wind, or in very cold weather, or after the furnace has run for a while.
- Note whether there is standing water near the furnace.
How to fix it
- Clear any obstruction at the terminations.
- The measurements Lennox specifies are technician work, and they are what separates a marginal inducer from a marginal switch.
- Resist replacing the pressure switch first. On this code the switch has already demonstrated it can close.
Notes
A fault that appears only sometimes is often assumed to be electrical or intermittent. Here it usually is not — it is a real physical restriction that only matters once the furnace is running.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.
The three E22x codes, told apart by timing
The 508565-01 table gives this furnace three pressure switch codes, and the entire difference between them is when the switch was in the wrong state:
| Code | When the control objected | What it implies |
|---|---|---|
| E223 | Switch never closed after the inducer started | Draft was never proved — blockage, weak inducer, or a failed switch |
| E224 | Switch already closed before the inducer started | The interlock cannot prove anything — stuck contacts or a wiring short |
| E227 | Switch closed, then opened during ignition or run | Draft existed and was lost — something marginal, not something broken |
All three share one action block in the manual — check the closing pressure on a heat call, measure operating pressure in inches w.c., inspect the vent and inducer for restriction — but E227 is the only one where the switch has already demonstrated it can do its job, which reorders the suspect list toward the vent, the condensate path and the inducer.
What the fix costs
Pressure switch work runs $150–400 in the repair cost guide, but on E227 specifically the switch is the least likely purchase — this code certifies it closed once already, so paying $150–400 to replace it on spec is the classic wasted repair here. The likelier money goes to whatever is marginal: nothing (a cleared termination or drain), or the inducer at $300–900 when the measurements show it starting strong and fading under load. The guide's blocked-flue-first note applies double on a closed-then-opened fault. More codes like this across brands: pressure switch codes.
DIY or call a pro
The homeowner checks for E227 are about partial restriction, which is easy to miss when you are looking for blockage: a termination half-occluded by ice or vegetation passes a glance but fails under load, so look closely at both pipes, and note the conditions — wind direction, deep cold, how long the furnace had been running — each time the code appears, because a pattern in those notes is half the diagnosis. The manometer comparison Lennox specifies (closing pressure versus actual operating pressure) is the professional half; it is the only way to separate a fading inducer from a marginal switch, and guessing between them costs real money in the wrong order. Do not jumper the switch to ride through the fault: E227 means the flue proved itself and then stopped being able to, mid-burn, which is precisely the situation the interlock exists for.
What this looks like
From the outside, this usually shows up as the furnace turns over but never lights — that walkthrough covers what to check in order, and when it stops being a homeowner job.