Goodman GMSS960803BN Error Code 1 Flash: System Lockout
What Does Code 1 Flash Mean?
One flash on the Goodman GMSS960803BN diagnostic LED indicates a system lockout due to an excessive number of ignition retries (3 total). The furnace attempted to light three times and either failed to establish a flame or lost the flame shortly after it was established. The system automatically locks out for one hour before retrying.
During each ignition attempt, the hot surface igniter heats up to light the gas, and the flame sensor must detect the flame within a few seconds. If the sensor does not register a flame, the gas valve closes and the system retries. After three failed attempts, the control board enters lockout.
The most common cause is a dirty or oxidized flame sensor. Even when the burners ignite properly, a coated sensor cannot generate enough electrical current to confirm flame presence, so the control board shuts off the gas. Other causes include no gas supply, a bad or misaligned igniter, a stuck front cover pressure switch, or interrupted gas supply causing lazy burner flames.
Common Causes
When to Call a Professional
Contact a licensed HVAC technician if:
- The lockout returns after cleaning the flame sensor
- The igniter does not glow at all during the ignition sequence
- The burners never light (no flame visible through the sight glass)
- Other gas appliances in your home are also not working
- You smell gas but the burners do not ignite
✓ Verified against manufacturer service manual — March 2026