Goodman GMSS920803BN Error Code 1 Flash: System Lockout

What Does Code 1 Flash Mean?

One flash on the Goodman GMSS920803BN diagnostic LED signals a system lockout caused by an excessive number of ignition retries — three in total. On each attempt the Integrated Control Module runs the inducer, energizes the hot surface igniter, opens the gas valve, and then waits for the flame sensor to confirm a flame. If flame is never established, or is established and then lost, the board counts a retry. After the third failure it stops trying and locks out.

On this single-stage furnace the lockout is a safety response, not something to simply reset away. The most common triggers are no gas reaching the burners, a bad or misaligned hot surface igniter, and a coated or oxidized flame sensor that cannot prove the flame. A front-cover pressure switch that opens during the trial, lazy burner flames from improper gas pressure, or a restriction in the flue or combustion-air piping can also cause repeated flame loss.

This code sits at the end of a chain of related conditions on the same board. A 7-flash low-flame-signal warning often precedes it, indicating the flame sensor's microamp reading was already weakening while the furnace still ran. An 8-flash igniter-circuit fault points at the igniter specifically. The board automatically attempts to reset from lockout after one hour, so the furnace may run briefly and then lock out again until the underlying cause is corrected.

What You'll Notice

• The furnace tries to light — you hear the inducer and see the igniter glow — but shuts down, repeating up to three times
• After the third failed try the furnace goes quiet and does nothing for about an hour, then tries again
• No heat is delivered and the LED shows a repeating single flash
• The burners may light briefly and then go out (flame established, then lost)
• The problem often appears in cold snaps or after the furnace has sat unused

Common Causes

How This Is Diagnosed

A technician works the ignition sequence in order. First they confirm gas is actually reaching the furnace — checking the manual shutoff, the gas valve, and whether other gas appliances in the home work — because no gas to the burners is a leading cause. Next they observe the hot surface igniter for a proper glow and check its alignment and resistance, since a cracked igniter will not light the gas.

If the burners do light but the board still counts a failure, attention turns to flame proving: the flame sensor's microamp signal is measured and the rod is cleaned or repositioned as needed, and the front-cover pressure switch and gas pressure are checked for flames that light but then drop out. Because these steps involve the gas valve, igniter, and flame-sense circuit, they are service work rather than homeowner tasks.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• The furnace locks out with one flash and will not stay lit after the one-hour auto-reset
• The igniter glows but the burners never light
• The burners light and then go out within a few seconds every cycle
• Other gas appliances in the home are also not working, suggesting a gas-supply problem
• You smell gas at any point (leave the home first and call your gas company)

✓ Verified against manufacturer service manual — March 2026