Lennox SLP98UHV Error Code E 223: Low Pressure Switch Failed Open
What Does Code E 223 Mean?
Error code E223 on the Lennox SLP98UHV indicates that the low-fire pressure switch failed to close during a call for heat. The pressure switch is a safety device that verifies the combustion air inducer is creating sufficient draft to safely vent exhaust gases before the burners ignite.
When the inducer motor starts, it pulls air through the heat exchanger and out the exhaust vent, creating negative pressure. The low pressure switch senses this draft and closes its contacts. If the switch does not close, the SureLight Variable Capacity control blocks ignition and displays this error. The furnace will attempt to recover — if the low pressure switch fails, the furnace may try switching to the high-speed inducer to close both pressure switches and light on high fire (E229).
The most common cause is a blocked or restricted exhaust vent or combustion air intake. Ice buildup in winter is a frequent culprit, along with bird or insect nests, leaves, and other debris at the vent termination. Other causes include a failing inducer motor that cannot generate sufficient draft, or a cracked or disconnected pressure switch hose.
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 → |
When to Call a Professional
Contact a licensed HVAC technician if:
- The vents appear clear but E223 persists
- The inducer motor sounds weak, rattles, or does not start
- The pressure switch hose is intact but the switch still will not close
- You also see E271 (soft lockout from pressure switch failures)
- The vent run has excessive length or many elbows
✓ Verified against manufacturer service manual — March 2026