Lennox SLP98UHV Error Code E 226: High Pressure Switch Failed Closed
What Does Code E 226 Mean?
Error code E226 on the Lennox SLP98UHV means the high-fire pressure switch has failed in the closed position. Before the inducer motor starts, the SureLight Variable Capacity control expects the high-fire pressure switch to be open. Finding it already closed tells the board the switch cannot be trusted to prove draft, so it locks out ignition as a precaution.
This is a modulating furnace that proves draft at more than one firing rate, so it carries both a low-fire and a high-fire pressure switch. The high-fire switch operates at a higher draft threshold and verifies safe venting at full combustion output. When its contacts stick or weld closed, the board can no longer confirm that high-fire venting conditions are actually safe.
E 226 is a distinct failure mode within the pressure-switch family. It is the opposite of E 225, where the high-fire switch fails to close, and it is the high-fire counterpart of E 224, where the low-fire switch is stuck closed. Repeated pressure-switch trips during operation escalate the furnace to soft lockouts E 271 (pressure switch opening) and E 272 (pressure switch recycle).
What You'll Notice
- The furnace will not start and displays E 226 in the diagnostic history
- The burners never light, so there is no heat
- The code can appear suddenly with no prior venting complaints
- You may see both E 224 and E 226, pointing to a broader pressure-switch problem
- The furnace stays locked out until the switch is serviced
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Pressure switch contacts stuck or welded closed | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician tests the high-fire pressure switch for continuity with the inducer off. Finding the contacts closed when they should be open confirms the switch has failed closed and needs replacement.
The technician also inspects the pressure tubing for moisture or condensate and checks the inducer for excessive vibration, since either can contribute to a switch sticking. When both the low-fire and high-fire switches read closed, they look for a common cause such as moisture in the shared tubing routing rather than assuming two independent failures. Continuity 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 furnace will not start and displays E 226
- The code appeared suddenly with no prior venting issues
- Both E 224 and E 226 appear together, suggesting a broader pressure-switch problem
- The code returns after power has been cycled
Frequently Asked Questions
What does 'stuck closed' mean for the high-fire switch?
The high-fire pressure switch should be open at rest and close only when the inducer produces strong high-fire draft. Stuck closed means it stays shut even with the inducer off, so the board cannot use it to prove safe venting and blocks ignition.
Why might I see both E 224 and E 226?
Seeing the low-fire (E 224) and high-fire (E 226) switches both stuck closed often points to a shared cause, such as moisture in the pressure tubing, rather than two separate switch failures. A technician looks for that common source.
Can I just reset the furnace?
Cycling power may clear the display briefly, but a switch that has genuinely failed closed will trigger the code again. The switch needs to be tested and replaced by a qualified technician.
✓ Verified against manufacturer service manual — March 2026