Furnace pressure switch codes on every brand

More fault codes point at the pressure switch than at any other part of a furnace. Here is what each manufacturer's pressure switch codes mean, and why the same switch produces two opposite faults.

What the pressure switch does

The pressure switch is a safety interlock that proves the inducer is actually moving air before the control will open the gas valve. It is a simple diaphragm switch connected by a small hose to the inducer housing or the vent. Suction from a running inducer pulls the diaphragm over and closes the contacts; with no suction the contacts sit open.

Why one part produces several different codes

That is why every manufacturer reports two different pressure switch faults rather than one. Stuck open means the inducer is running but the switch never closed — usually a blocked vent or intake, a cracked or disconnected hose, water in the hose or the collector box, or a failed inducer. Stuck closed means the switch was already closed before the inducer started, which the control reads as a switch that cannot prove anything and therefore cannot be trusted. The first is far more common in cold weather; the second normally means a failed switch or a shorted circuit.

Every pressure switch code on this site

35 codes across 10 control families. The meaning is the manufacturer's, from the document listed at the foot of each code page.

Brand	Code	What it reports
Armstrong	10 flashes	Watchguard — pressure switch opened five times during one heat demand
Armstrong	11 flashes	Pressure switch stuck closed before the inducer started
Armstrong	9 flashes	Pressure switch failed to close, or opened during a heat demand
Carrier	Status code 23	Pressure switch did not open
Carrier	Status code 31	Pressure switch did not close, or reopened
Goodman	2 flashes	Pressure switch is closed when it should be open
Goodman	3 flashes	Pressure switch will not close
Goodman	9 flashes	High stage pressure switch stuck open
Goodman	E1	Low stage pressure switch closed at the start of the heating cycle
Goodman	E2	Low stage pressure switch stuck open
Goodman	E8	High stage pressure switch closed at the start of the heating cycle
Goodman	E9	High stage pressure switch stuck open
Goodman	2 red flashes	Pressure switch stuck closed, or an inducer error
Goodman	3 double red flashes	Second stage pressure switch stuck open, or an inducer error
Goodman	3 red flashes	First stage pressure switch stuck open, or an inducer error
Goodman	6 red flashes	Pressure switch cycle lockout
Heil	2 flashes	Low pressure switch closed when it should be open
Heil	3 flashes	Low pressure switch still open 30 seconds after the inducer started
Heil	6 + 2 flashes	Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
Heil	8 flashes	High pressure switch closed when it should be open
Heil	9 flashes	High pressure switch open when it should be closed
Lennox	Alert code 223	Low pressure switch open
Lennox	Alert code 226	High pressure switch stuck closed
Lennox	Alert code 227	Low pressure switch open in run mode
Lennox	Alert code 271	Low pressure switch open — Watchguard
Lennox	Alert code 272	Low pressure switch open in run mode — Watchguard
Lennox	Alert code 276	Furnace calibration failure, or high pressure switch fault
Rheem	2 blinks	Pressure switch did not close within 10 seconds
Rheem	3 blinks	Pressure switch closed when it should be open
Rheem	2 blinks	Pressure switch failure — switch remains open
Rheem	4 blinks	Pressure switch failure — switch remains closed
York	2 red flashes	Pressure switch stuck closed, or an inducer error
York	3 double red flashes	Second stage pressure switch stuck open
York	3 red flashes	Pressure switch open, or first stage pressure switch open
York	6 red flashes	Pressure switch cycle lockout

Before you work on it

A pressure switch that will not close is often the furnace correctly refusing to fire because the flue is blocked. Bypassing or jumpering it defeats the interlock that prevents combustion products entering the house.

Other parts

Sources

Every code meaning above comes from the manufacturer document behind its code page:

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.