A Lennox furnace pressure switch code means the furnace couldn’t prove its venting was clear, so it won’t light. On a Signature or Elite furnace it shows as E223 or E227; on a Merit ML180UHE it’s 9 red flashes. The switch is rarely the broken part. It’s telling you the vent, the drain or the inducer has a problem. A repair starts with our $99 diagnostic, and clearing a clogged condensate drain with a trap and switch added is $175 to $420.
Every Lennox code, and every repair price, is on our Lennox repair page.
Lennox pressure switch codes
| Code | Furnace | What it means |
|---|---|---|
| E223 | Signature and Elite (SLP99V, SL280V, EL296V) | Low pressure switch failed open |
| E224 | Signature and Elite | Low pressure switch failed closed |
| E225 | Signature and Elite | High pressure switch failed open |
| E227 | Signature and Elite | Low pressure switch opened during ignition or while running |
| E271 | Signature and Elite | Soft lockout: the last retry failed because the pressure switch opened |
| 9 flashes | Merit ML180UHE | Pressure switch failed to close, or opened during heat |
| 3 flashes | Merit ML296V | Pressure switch open with the inducer running |
From Lennox’s SL280UHVK instructions and ML180UHE unit information.
What the pressure switch is actually telling you
Before the burners light, the inducer fan pulls air through the furnace and out the vent. The pressure switch proves that draft is there. When it can’t, the cause is almost always upstream of the switch:
A blocked vent or intake. On a high-efficiency furnace the white PVC pipes go out a wall or the roof. Snow, leaves, a nest or a crushed screen will do it.
Water where it shouldn’t be. A 90%+ furnace makes water, and a clogged trap or drain backs it up into the pressure switch’s world. On many installs the AC coil shares that drain, so a summer of cooling can clog it before the first cold night.
The hose. A cracked, kinked or water-filled pressure tube between the switch and the inducer.
The inducer itself. A motor that’s slowing down can’t make enough draft.
Replacing the switch without fixing those just moves the same code to next week.
What you can check yourself
Go outside and look at the two PVC pipes: clear anything blocking them. Check the filter. If the furnace has a clear drain hose, look for standing water in it. Then turn the furnace off and on once. If the code comes back, call, and don’t keep resetting it.
Lennox pressure switch questions people ask us
What does E223 mean on a Lennox furnace?
The low pressure switch failed open: the furnace couldn’t prove its draft, so it won’t light. Usually a blocked vent, a clogged condensate drain, a bad hose or a weak inducer. The diagnostic is $99.
Can I bypass the pressure switch on my Lennox?
No. It’s a safety that keeps the furnace from running when its exhaust can’t get out, and bypassing it can put carbon monoxide in the house.
How much does it cost to fix a Lennox pressure switch problem?
It depends on the cause, which is why the diagnostic comes first. A clogged condensate drain cleared, with a trap and float switch added, is $175 to $420. If the furnace itself is done, a new one is $4,285 to $14,040 installed. From about $71 a month at 0% APR for 60 months, the whole price financed, on approved credit.
Do you work on Lennox furnaces?
Yes, every Lennox: Merit, Elite and Signature. See the Lennox repair page.
