Lennox SLP98UHV Error Code E 223: Low Pressure Switch Failed Open
What Does Code E 223 Mean?
Error code E223 on the Lennox SLP98UHV means the low-fire pressure switch failed to close during a call for heat. This switch is a safety device that proves the combustion air inducer is pulling enough draft to vent exhaust gases safely before the burners are allowed to ignite.
Because the SLP98UHV is a modulating furnace, it proves draft at more than one firing rate and carries two switches: a low-fire pressure switch for the lower combustion rate and a separate high-fire pressure switch for full output. E 223 is specific to the low-fire switch failing to close. When the inducer starts, it should create enough negative pressure to close this switch; if the switch stays open, the SureLight Variable Capacity control blocks ignition and displays the code rather than firing without proven draft.
The most common cause is a blocked or restricted exhaust vent or combustion air intake — winter ice at the termination, bird or insect nests, leaves, or other debris. Other causes include a failing inducer motor that cannot generate enough draft, or a cracked or disconnected pressure switch hose. Repeated failures of the pressure-switch family escalate to soft lockouts: E 271 (pressure switch opening) and E 272 (pressure switch recycle).
What You'll Notice
- The inducer motor runs but the burners never light, so there is no heat
- The furnace tries to start, then shuts down and retries without igniting
- The 7-segment display shows E 223 in the diagnostic error history
- Symptoms are worse in cold weather when ice can form at the vent termination
- Repeated failed attempts may end in a no-heat lockout
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted exhaust vent preventing proper draft | Most common | ✗ Call a pro → |
| Failed or weak combustion air inducer motor | Common | ✗ Call a pro → |
How This Is Diagnosed
A homeowner-safe first check is to look at the exhaust and intake vent terminations outside for ice, snow, leaves, or nests, since a blocked vent is the most common cause and clearing it is low risk. If the terminations are clear and the code returns, the problem moves to the technician.
A technician measures the actual draft pressure in inches of water column while the inducer runs and compares it to specification, which separates a venting restriction from a weak inducer or a faulty switch. They also inspect the pressure switch hose for cracks, kinks, or moisture, and check the full vent run for restrictions. Pressure measurement, inducer testing, and switch replacement are pro-only tasks.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The vent and intake terminations outside are clear but E 223 keeps returning
- The inducer motor sounds weak, rattles, or does not start
- The pressure switch hose looks intact but the switch still will not close
- You also see E 271 or E 272 (soft lockouts from repeated pressure switch failures)
- The vent run is very long or has many elbows and the furnace struggles to light
Frequently Asked Questions
Is there anything safe I can check myself before calling a technician?
Yes. You can safely inspect the exhaust and intake vent terminations outside for ice, snow, leaves, or animal nests and clear away any obstruction. Anything inside the furnace, including pressure testing and the switch itself, should be left to a technician.
Why does E 223 happen more often in winter?
Cold weather can allow ice and frost to build up at the vent termination, restricting the draft the inducer needs to close the low-fire pressure switch. Clearing the ice sometimes resolves it, but a recurring code needs professional diagnosis.
What is the difference between E 223 and the high-fire pressure switch code?
E 223 is the low-fire pressure switch failing to close, while E 225 is the high-fire pressure switch failing to close on this two-switch modulating furnace. They involve different switches and different firing rates, though both often trace back to a venting or inducer problem.
✓ Verified against manufacturer service manual — March 2026