Goodman furnace 3 flashes: Pressure switch will not close

Three flashes means the draft inducer started and the pressure switch did not close, so the control never released gas. Something is preventing the furnace from proving it can vent.

Applies to: Goodman GMS, GMP, GMH, GMV8, GMV9 and Amana AMH, AMV9 series gas furnaces with a single red diagnostic LED. On Goodman GMSS9 and Amana AMSS9 the same flash count is described as the pressure switch circuit not being closed.

What it means

At the start of a heating cycle the control runs the draft inducer and waits for the pressure switch to close, confirming the inducer is moving enough air to carry combustion products safely out of the house. If the switch does not close within the allowed time, the sequence stops before the gas valve ever opens. This is the single most common fault code on high-efficiency furnaces, and the reason is that everything in the venting path can cause it — a blocked intake or exhaust, a full condensate trap, a weak inducer, a disconnected hose. It is also the fault most often caused by something outside the furnace entirely, such as a vent terminal blocked by snow, ice, or a bird's nest.

Most common causes

A blocked exhaust or intake pipe. Snow, ice, leaves, insect nests, and rodent nests at the outside termination are all common.
A condensate drain or trap that is full or blocked, so water sits where the draft should be.
The sensing hose to the pressure switch is disconnected, cracked, kinked, or full of water.
The draft inducer motor is weak, seized, or its wheel is loose, so it cannot generate the required suction.
The pressure switch itself has failed and no longer closes at its rated pressure.
Vent piping that is too long, has too many elbows, or was installed at the wrong diameter for the furnace's input.
High wind at the vent termination, which can briefly disturb the draft on some installations.

How to diagnose it

Go outside and look at the vent termination first. This is the highest-yield check on the whole list and needs no tools — a pipe packed with snow or a nest explains the fault completely.
Listen for the inducer motor. If it does not run at all, the fault is upstream of the pressure switch. If it runs and the furnace still does nothing, the switch is not seeing the draft.
Check the condensate drain line and trap for standing water or blockage, and look for water spilling anywhere inside the cabinet.
Note the weather. This fault appearing during the first hard freeze or a snowstorm points strongly at the termination.
Check whether anything was recently built, planted, or stored near the outside vent.

How to fix it

Clear the vent termination if it is blocked. Keep snow, ice, and vegetation clear of both pipes, and check them after heavy weather.
Clear a blocked condensate drain, which is a reasonable homeowner task on most installations.
The pressure switch, its hose, the inducer motor, and the vent system inside the cabinet belong to a technician.
If the vent piping is undersized or over-length for the furnace, it needs correcting rather than working around. A furnace that only just manages to prove draft will fault intermittently for years.
Never bypass the pressure switch. It is the interlock that prevents the furnace firing into a blocked flue, and a blocked flue with a firing burner is how carbon monoxide enters a house.

Notes

If this fault appears on the coldest night of the year and clears on a milder day, suspect ice at the vent termination rather than a component failure. High-efficiency furnaces produce condensate at the exhaust, and it can freeze around the pipe and progressively close it.

All codes for this manufacturer

Goodman and Amana furnace fault codes — every code, with what differs between models.

Not sure this is your brand?

The same count means something else on other furnaces. What 3 flashes means on every brand puts them side by side.

This code is not a homeowner repair. Faults in this group involve the gas valve, the burner compartment, or the heat exchanger — the parts whose failure can put combustion products, including carbon monoxide, into the air the house breathes. Do not reset it repeatedly to keep the heat on. Have it looked at by a licensed technician, and make sure there is a working carbon monoxide alarm on every level of the home, including the level the furnace is on.

Sources

Goodman Manufacturing — Diagnostic Code Identification System (model-specific fault code lookup)

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.