HeatingCodes

Furnace pressure switch error: what the code means and what to check

By Jason Dearmin · Last reviewed November 14, 2026 · How we check facts

Short answerA furnace pressure switch code means the control saw the switch in the wrong position: open when the draft inducer should have pulled it closed (the common case), or closed when it should be open. Across the twelve manufacturer manuals we compared, the causes come from the same short list: a blocked or restricted vent or intake, a pinched, blocked or disconnected pressure hose, a blocked condensate drain on high-efficiency furnaces, wind, a weak inducer, or, less often than people think, the switch itself.

What the pressure switch does

Before a modern gas furnace lights its burners, a small fan called the draft inducer starts and pulls air through the heat exchanger and out the vent. The pressure switch is connected to that system by a rubber hose and closes only when the inducer creates enough suction. If the switch does not close, the control will not open the gas valve. That is a safety feature: it keeps the burners off when combustion gases may not be venting properly.

Pressure switch codes by brand

Brand and seriesCodeMeaning in the manufacturer documentDocument
Carrier / Bryant two-stage (352MAV, 59TP6A, 926TB)32Low-heat pressure switch did not close or reopenedSP05-59, 59TP6A-10SI, II926TB-01
Carrier / Bryant two-stage31High-heat pressure switch or relay did not close or reopenedSame
Carrier / Bryant two-stage43Low-heat pressure switch open while high-heat pressure switch is closedSame
Carrier single-stage (59SC5A, 58SC0A)31Pressure switch (LPS or HPS on 59SC5A) did not close or reopened59SC5A-13SI, 58SC0A-05SI
Carrier / Bryant (all five)23Pressure switch did not openAll five Carrier and Bryant guides
Trane / American Standard LED boards3 flashesDraft pressure error18-CH49D1-1
Trane S9V2, S9X1, S9X2, S9B1E3.2 (E3.4 for 2nd stage)Pressure switch open when it should be closedFNR-SVX001C-EN, FNR-SVX002B-EN
Trane S9V2, S9XE3.1 (E3.3 for 2nd stage)Pressure switch closed when it should be openSame
Goodman / Amana 96% (34.5" chassis)EE2 / EE9Low-stage / high-stage pressure switch openRS6612023
Goodman / Amana 96%EE1 / EE8Low-stage / high-stage pressure switch stuck closedRS6612023
Lennox SL280DFVE223 / E225Low / high pressure switch failed open508246-01
Lennox SL280DFVE227, E271, E272Low pressure switch open during ignition or run; soft lockouts after the pressure switch opened508246-01
Rheem / Ruud 801T, 80MSX57 / 55Pressure switch stuck open / stuck closed92-24161-144-08
York TM9V3 red / 2 redPressure switch contacts open when they must be closed / closed when they must be open5750149-UIM-I-0423
York TM9V6 red, 13 redPressure switch opened four times in one call for heat (1-hour lockout); high-fire pressure switch openSame

Most of these tables come from documents for specific series. If your furnace is a different series, use the label inside your furnace door or its manual; codes can change between boards even within one brand.

Open versus closed: two different problems

Switch open when it should be closed (Carrier 31/32, Trane E3.2, Goodman EE2, Lennox E223, Rheem 57, York 3 red) is by far the more common pattern. The inducer is running, but the switch is not seeing enough suction. Switch closed when it should be open (Carrier 23, Trane E3.1, Goodman EE1, Rheem 55, York 2 red) is checked before the inducer starts. Carrier lists an obstructed pressure tube or a switch stuck closed; Goodman lists a sticking switch or a short in the switch wiring; York lists a faulty switch or miswiring.

What the manuals say causes "switch open"

Carrier also checks gas pressure Carrier's 31 and 32 check lists include low inlet gas pressure "if LGPS used", meaning furnaces fitted with an optional low gas pressure switch wired into the same circuit.

Safe checks for a homeowner

  1. Write down the code exactly, and the furnace model number from the rating plate, before you turn anything off. Some controls, for example Carrier red-LED boards, erase stored codes when power is interrupted.
  2. Go outside and find where the furnace pipes leave the house (usually two plastic pipes on a high-efficiency furnace, or a metal flue through the roof on an 80% furnace). Clear snow, ice, leaves or nests you can reach safely from the ground. Do not climb onto the roof or take pipes apart.
  3. Indoors, look without touching anything electrical: is the rubber hose from the pressure switch visibly off its fitting, or is there water in a clear condensate tube or pooling under the furnace? Note what you see for the technician.
  4. If it is very windy, note it. Wind is a listed cause.
  5. Restart once by turning the thermostat off for a few minutes and back to heat. If the code returns, call a licensed heating technician.

When to stop and call

Never jumper a pressure switch Bypassing a pressure switch can let a furnace fire when exhaust gases are not venting, which is a carbon monoxide risk. If a CO alarm sounds, get everyone outside and call 911. If you smell gas, leave and call your gas utility from outside.

Safe homeowner checks for a furnace pressure switch code

  1. Record the code and modelWrite down the flash pattern or display code and the furnace model number before cutting power.
  2. Clear the outdoor vent and intakeFrom the ground, clear snow, ice and debris from the furnace exhaust and intake terminations.
  3. Look for obvious hose or water problemsWithout touching wiring, look for a disconnected pressure switch hose or water pooling or trapped in tubes, and note it.
  4. Restart onceTurn the thermostat off for a few minutes, then back to heat. If the code returns, call a technician.

Frequently asked questions

Can a dirty filter cause a pressure switch error?

None of the pressure switch check lists in these documents names the air filter. A dirty filter is listed for limit codes instead (for example Carrier 33, Trane 4 flashes or E04). Change it anyway if it is dirty, but look at the vent and condensate for a pressure switch code.

Why does my furnace pressure switch error happen only when it is very cold or windy?

Wind is a listed cause in the Carrier and Trane documents, and snow or ice at the vent terminations restricts the vent. Both are worse in winter storms.

Is it the pressure switch or the inducer?

A technician tells them apart by measuring the suction at the switch and comparing it with the value printed on the switch label, which is the step in Trane's flow chart. If suction is low, the problem is the vent, hose, drain or inducer, not the switch.

Sources

Related

Carrier furnace status code 32Trane furnace error E3.2Goodman and Amana furnace code EE2Lennox furnace code E223York TM9V furnace 3 red flashesHow to read your furnace blinking light code

Safety note: this page is general information drawn from the sources above. Gas, combustion and line-voltage repairs belong to a licensed professional. Your own equipment's label and manual take priority over anything here. Read the full disclaimer.