Lennox SLP98UHV Error Code E 227: Low Pressure Switch Open During Run

What Does Code E 227 Mean?

Error code E227 on the Lennox SLP98UHV means the low-fire pressure switch opened during the trial for ignition or during active run mode. In other words, the furnace initially had enough draft to close the switch, but during operation the draft weakened or fluctuated enough for the switch to drop open again.

This switch is a safety device that continuously proves the combustion air inducer is maintaining adequate draft. When it opens mid-cycle, the SureLight Variable Capacity control immediately shuts off the gas valve and stops the ignition sequence. That is a critical protection: without proven draft, combustion gases could spill into the home instead of venting outside. Because this is a modulating furnace with both low-fire and high-fire switches, E 227 is specific to the low-fire switch opening during the cycle, as opposed to E 223, where the low-fire switch never closes in the first place.

Common causes include intermittent vent blockages such as wind gusts pushing back against the exhaust, condensate collecting in the vent pipe or pressure tubing, or a weakening inducer motor that cannot hold steady draft. In cold climates, ice forming in the vent during a cycle is a frequent culprit. Repeated mid-cycle openings escalate the furnace to soft lockouts E 271 (pressure switch opening) and E 272 (pressure switch recycle).

What You'll Notice

• The furnace lights, then shuts down partway through the heating cycle
• Shutdowns happen more often on windy or very cold days
• The furnace short-cycles, repeatedly starting and stopping without steady heat
• The 7-segment display shows E 227 in the diagnostic error history
• You may notice water or ice in or around the exhaust vent termination outside

Common Causes

How This Is Diagnosed

A homeowner-safe first check is to look at the exhaust and intake vent terminations outside for ice, water, or debris, since intermittent blockage and wind effects are common triggers. If the terminations look clear and the code keeps returning, diagnosis moves to the technician.

A technician measures the draft pressure in inches of water column while the furnace runs, watching for the pressure to sag or fluctuate toward the switch's opening point. They inspect the full vent run for restrictions, condensate traps, or improper slope, check the pressure tubing for water, and evaluate whether the inducer can hold steady draft. Pressure measurement, inducer testing, and switch service 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 starts but shuts down partway through the heating cycle with E 227
• The code appears primarily during windy or very cold weather
• You notice water or ice in or around the exhaust vent termination outside
• The vent terminations look clear but the furnace still short-cycles
• You also see E 271 or E 272 (soft lockouts from repeated pressure switch openings)

✓ Verified against manufacturer service manual — March 2026