Goodman furnace 1 flash: Lockout after too many failed ignition attempts

One flash means the furnace tried to light, failed, tried again, and has now stopped trying. It is a lockout, not a single failure — the control has already made every attempt it is allowed.

Applies to: Goodman GMS, GMP, GMH, GMV8, GMV9 and Amana AMH, AMV9, AMSS9 series gas furnaces with a single red diagnostic LED. Later communicating boards show this condition as code E0 instead.

What it means

The control gives the furnace a fixed number of ignition attempts, normally three, and counts each one that does not end with a proven flame. When the count runs out it stops calling for gas and reports the lockout. That distinction matters when reading the code: the furnace is not failing to light right now, it failed repeatedly a short time ago and has taken itself out of service deliberately. Most controls clear the lockout automatically after about an hour and try again, which is why a furnace with this fault often appears to work for one cycle and then quit — it is not recovering, it is retrying on a timer. The underlying cause is almost always either no gas reaching the burners, no ignition source, or a flame that lit but was not detected.

Most common causes

The gas supply is off or interrupted — a closed manual valve, an empty propane tank, or a utility outage.
The hot surface igniter has failed or cracked, so nothing is lighting the gas.
The flame sensor is coated with oxide, so the flame lights and the control cannot see it and shuts the gas off.
The flame sensor is bent out of the flame path, with the same result.
The gas valve is not opening, or the manifold pressure is too low to establish a stable flame.
Poor electrical grounding, which prevents the flame rectification signal from being read even when everything else is correct.
A blocked or partly blocked flue restricting combustion enough that the flame will not stabilise.

How to diagnose it

Confirm the code by counting the flashes through the sight glass, waiting for the pause, and counting again. A miscount sends you to the wrong fault entirely.
Check that other gas appliances in the house are working. If nothing gas-fired works, the problem is the gas supply and not the furnace.
Check the furnace's own shutoff valve is open and, on propane, that the tank is not empty.
Watch a full cycle through the sight glass if you can do so with the panel in place. Whether the burners light at all separates an ignition problem from a flame-sensing problem — if they light and go out after a few seconds, the flame is being lost rather than never made.
Reset by switching the furnace off at its service switch for about thirty seconds, then on, and watch one complete attempt.

How to fix it

Restore the gas supply if that is the cause — reopen a valve that was closed, or refill the tank.
Replace the air filter and confirm supply registers are open. Restricted airflow does not cause this directly but it accompanies enough other faults to be worth eliminating first.
Everything else on this list belongs to a technician. Cleaning a flame sensor, replacing an igniter, testing manifold pressure, and checking the gas valve all involve the flame-sensing circuit, the gas train, or both.
Do not repeatedly reset the furnace to force it to run. Each reset starts another sequence that delivers gas to a burner that may not light it, and repeated unburned gas cycles are exactly what the lockout exists to stop.

Notes

A furnace that lights, runs a few seconds, then shuts off and eventually locks out is the classic dirty flame sensor. It is one of the most common causes of this code and one of the cheapest repairs, but it sits in the flame-sensing circuit, which is a licensed technician's work.

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 1 flash 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

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.