Goodman furnace 5 flashes: Flame detected when no flame should be present

Five flashes means the control is seeing a flame at a moment when the gas valve should be closed. Either gas is still burning when it should not be, or the sensing circuit is reporting a flame that is not there.

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 worded slightly differently, as flame sensed with no call for heat — the same condition, described from the thermostat side.

What it means

The control watches the flame sensor continuously, not only while the burners are meant to be lit. If it detects flame while the gas valve is commanded closed, it reports this fault and normally runs the draft inducer to clear any unburned gas from the heat exchanger. The reason this is treated seriously is that one of its two possible causes is a gas valve that is not fully closing, which means gas entering the combustion chamber outside a controlled cycle. The other cause is electrical — a short in the flame sensor wiring can produce a signal indistinguishable from a real flame. The control cannot tell these apart, so it assumes the dangerous one.

Most common causes

A gas valve that is leaking through or not closing fully, so a small flame persists after the cycle ends.
A slow-closing gas valve, where flame lingers briefly after shutdown and is caught by the check.
A short to ground in the flame sensor wiring or at the sensor itself.
A damaged or chafed flame sensor wire touching the cabinet.
A failed control board misreading the flame signal.
Residual flame on a burner after the main flame is cut, which can indicate a burner or manifold problem.

How to diagnose it

Confirm the count. This is one of the codes where an accurate count genuinely changes what happens next.
Note whether the draft inducer runs continuously without the furnace heating. That behaviour accompanies this fault and is the control purging the heat exchanger.
Do not open the burner compartment to look for flame while the furnace is powered. There is no safe homeowner check for this fault.
Note any smell of gas. If you can smell gas, stop diagnosing — see the fix section.

How to fix it

If you smell gas: leave the building, do not switch anything electrical on or off, and call your gas utility's emergency line or the fire service from outside. Do not go back in to investigate.
If there is no gas smell, turn the furnace off at its service switch and leave it off until a licensed technician has looked at it.
This fault is entirely technician work. It involves the gas valve and the flame-sensing circuit, which are the two parts of a furnace a homeowner should never work on.
Do not reset repeatedly to see whether it clears. If the cause is a valve that is not closing, each reset is another opportunity for uncontrolled gas.

Notes

The wiring-short version of this fault is far more common than a leaking gas valve, and a technician will usually find it in minutes. That does not make it safe to assume — the control cannot distinguish them, and neither can anyone without test equipment at the valve.

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 5 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

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.