What causes Lennox Gas Furnace E223?

A blocked exhaust vent or combustion air intake pipe, for example a bird nest, debris, or snow and ice at the outside terminations (Lennox's own owner checklist says an obstructed flue will shut the unit off at the pressure switch). The combustion air inducer not starting or not running at full speed, such as a failing motor or bad bearings. A cracked, kinked, loose or water-filled pressure switch hose, or a hose on the wrong port. On 90%+ condensing models: a plugged or dry condensate trap, or a drain that backs up, so water collects in the cold end header box and upsets the pressure reading. On condensing models with the furnace and A/C coil drains tied together: an A/C drain outlet that isn't vented, which Lennox says keeps the furnace pressure switch from operating properly. Low supply voltage, which Lennox lists as an abnormal condition that can keep the low-fire switch from closing. A failed pressure switch or loose wiring between the switch and the control board.

How do I fix Lennox Gas Furnace E223?

Read the code on the furnace control's display (or on your Lennox thermostat as an alert). E223 is about the draft proving switch, not the flame or the ignitor. Go outside and look at the furnace's vent and intake pipes (on 90%+ furnaces these are usually two white PVC pipes through a wall or roof). Clear any snow, ice, leaves, nests or debris from the openings, and make sure nothing is stacked against them. Don't reach into or disassemble the venting itself. Turn the thermostat up and listen at the furnace. The inducer (the small fan motor on the burner side) should start first. If it doesn't start, hums, or makes grinding or squealing noises, that's a job for a technician. With power off at the furnace switch, look at the small rubber or silicone hoses running from the pressure switch. Check that they're pushed on firmly and aren't cracked, kinked or holding water. On a 90%+ furnace, check the condensate trap and drain line. A trap that is clogged, or a drain line that is kinked or doesn't slope downhill to the drain, can back water up. Lennox says the trap should be primed with water (about 10 fl. oz., or 300 ml) before start-up, which matters after a trap has been cleaned or the furnace sat unused and dried out. If your furnace drain and air conditioner coil drain share one line, check that there's an open vent on the A/C drain side. Lennox says the combined drain must be vented for the pressure switch to work properly. Restore power and call for heat. The code clears once the switch closes normally. Never jumper or bypass the pressure switch to get heat; Lennox says it is a safety shut-down control that must not be bypassed for any reason.

When should I call a pro for Lennox Gas Furnace E223?

The vents and drain are clear and E223 keeps coming back. A technician will tee a manometer into the switch hoses and measure the pressure differential, which Lennox says should be at least 0.15 in. w.c. above the switch's set point (the set points vary by model size and altitude). The inducer motor won't start, runs slowly, or is noisy. The pressure reading is good but the switch doesn't close, or the switch or its wiring needs replacing. Lennox says replacement switches must be the correct model-specific part, and the switch isn't adjustable. You also see E224, E225, E227, E271 or E229 repeatedly, or the furnace locks out. There's water inside the cabinet or the heat exchanger area, or the drain needs re-piping. You smell gas or exhaust: leave the house and call your gas utility from outside.

Code: E223🔥 Lennox Gas Furnace

Lennox Furnace Error Code 223 (E223): Low Pressure Switch Failed Open (Meaning, Causes, Fixes)

Reviewed 2026-10-23 · Based on 4 manufacturer & service sources

What the code means

Lennox unit information for SureLight two-stage furnaces such as the SL280UHVK and EL297UHE, and the EL296UHV(X) service literature, list E223 as "Low pressure switch failed open." The action column says to check the pressure (inches of water column) at which the low pressure switch closes on a heat call, measure the operating pressure, and inspect the vent and combustion air inducer for correct operation and restriction, and it notes the furnace resumes normal operation after the fault is cleared. The switch (S18 in Lennox literature) is a dual first- and second-stage proving switch on the inducer orifice bracket, connected by silicone hose. It closes when the inducer creates enough negative pressure, and its purpose is to prevent burner operation if the inducer isn't running or the flue is obstructed. When the proving switch opens, the control immediately closes the gas valve. Lennox notes that during abnormal conditions such as low supply voltage or low outdoor temperatures, if the low-fire switch does not close the inducer switches to high fire and the furnace lights on high fire, then drops to low fire after 10 to 20 seconds (on newer controls this is shown as information code E229). Related codes: E224 is the same switch stuck closed, E225 and E226 are the high pressure switch, E227 is the low switch opening during ignition or run, and E271 is a soft lockout after too many retries ended by the pressure switch opening. Lennox says the switch is factory set, not field adjustable, and must not be bypassed for any reason.

Likely causes

A blocked exhaust vent or combustion air intake pipe, for example a bird nest, debris, or snow and ice at the outside terminations (Lennox's own owner checklist says an obstructed flue will shut the unit off at the pressure switch)
The combustion air inducer not starting or not running at full speed, such as a failing motor or bad bearings
A cracked, kinked, loose or water-filled pressure switch hose, or a hose on the wrong port
On 90%+ condensing models: a plugged or dry condensate trap, or a drain that backs up, so water collects in the cold end header box and upsets the pressure reading
On condensing models with the furnace and A/C coil drains tied together: an A/C drain outlet that isn't vented, which Lennox says keeps the furnace pressure switch from operating properly
Low supply voltage, which Lennox lists as an abnormal condition that can keep the low-fire switch from closing
A failed pressure switch or loose wiring between the switch and the control board

Safe DIY checks

⚠ Before you start

Turn off power at the furnace/HVAC service switch and the breaker before opening panels. Shut the gas valve before any work near the burners, and never disconnect or alter the gas line. If you smell gas, leave the house and call your gas utility.

Read the code on the furnace control's display (or on your Lennox thermostat as an alert). E223 is about the draft proving switch, not the flame or the ignitor.
Go outside and look at the furnace's vent and intake pipes (on 90%+ furnaces these are usually two white PVC pipes through a wall or roof). Clear any snow, ice, leaves, nests or debris from the openings, and make sure nothing is stacked against them. Don't reach into or disassemble the venting itself.
Turn the thermostat up and listen at the furnace. The inducer (the small fan motor on the burner side) should start first. If it doesn't start, hums, or makes grinding or squealing noises, that's a job for a technician.
With power off at the furnace switch, look at the small rubber or silicone hoses running from the pressure switch. Check that they're pushed on firmly and aren't cracked, kinked or holding water.
On a 90%+ furnace, check the condensate trap and drain line. A trap that is clogged, or a drain line that is kinked or doesn't slope downhill to the drain, can back water up. Lennox says the trap should be primed with water (about 10 fl. oz., or 300 ml) before start-up, which matters after a trap has been cleaned or the furnace sat unused and dried out.
If your furnace drain and air conditioner coil drain share one line, check that there's an open vent on the A/C drain side. Lennox says the combined drain must be vented for the pressure switch to work properly.
Restore power and call for heat. The code clears once the switch closes normally. Never jumper or bypass the pressure switch to get heat; Lennox says it is a safety shut-down control that must not be bypassed for any reason.

🛠 When to call a pro

The vents and drain are clear and E223 keeps coming back. A technician will tee a manometer into the switch hoses and measure the pressure differential, which Lennox says should be at least 0.15 in. w.c. above the switch's set point (the set points vary by model size and altitude).
The inducer motor won't start, runs slowly, or is noisy.
The pressure reading is good but the switch doesn't close, or the switch or its wiring needs replacing. Lennox says replacement switches must be the correct model-specific part, and the switch isn't adjustable.
You also see E224, E225, E227, E271 or E229 repeatedly, or the furnace locks out.
There's water inside the cabinet or the heat exchanger area, or the drain needs re-piping.
You smell gas or exhaust: leave the house and call your gas utility from outside.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Furnace pressure switch (model-specific Lennox part)

Only after a manometer test shows the switch, not the vent or inducer, is the problem. Match the part number from your furnace's Lennox repair parts list.

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⚙

Pressure switch hose

For a cracked, hardened or kinked hose between the switch and the header box.

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⚙

Manometer (pressure gauge)

What Lennox's pressure switch check uses to measure the differential against the set-point tables.

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Sources

Last reviewed 2026-10-23. Always confirm against the manual for your exact model number.