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.