Lennox SLP98UHV Error Code E 225: High Pressure Switch Failed Open
What Does Code E 225 Mean?
Error code E225 on the Lennox SLP98UHV indicates that the high-fire pressure switch failed to close during a call for heat. The SLP98UHV is a variable-capacity furnace with both low-fire and high-fire pressure switches. The high pressure switch requires greater draft than the low pressure switch, as it must verify safe venting at the higher combustion rate.
When the inducer motor runs at high speed for high-fire operation, it creates a stronger vacuum. The high pressure switch senses this increased draft and closes to allow high-fire ignition. If only the high switch fails but the low switch closes, the furnace may still be able to operate on low fire. However, if neither switch closes, the furnace will not ignite at all.
The most common cause is a partial blockage in the exhaust vent or combustion air intake that is enough to prevent the higher draft threshold from being reached. Even a small restriction — such as a partially blocked vent screen, a slight ice buildup, or debris partially obstructing the pipe — can cause the high pressure switch to fail while the low switch still operates. A failing inducer motor losing its ability to reach full speed is another common cause.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blocked or restricted exhaust vent preventing proper draft at high fire | Most common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- E225 persists after clearing all visible vent blockages
- The inducer motor sounds different at high speed compared to low speed
- The furnace runs on low fire but cannot switch to high fire
- The pressure switch hoses are intact but the high switch will not close
- You also see E271 or E272 (soft lockout codes related to pressure switches)
✓ Verified against manufacturer service manual — March 2026