Goodman single-stage gas furnace fault codes (GMS8, GDS8, GHS8, GMS80, GDS80, GHS80)
Every fault code for this Goodman single-stage gas furnace is below, with what it indicates and a verdict: whether you can safely check it or it is a call for a technician. Here the code is a count of LED flashes. The source is Goodman's own service manual. Confirm your model is on the list; other Goodman controls use different codes.
Before any code: if you smell gas or a carbon monoxide alarm is sounding, this is not a diagnostic exercise. Leave the house and call from outside. What to do about a gas smell or a CO alarm.
How to read the display
These single-stage models do not show letters and numbers. A single red diagnostic LED on the control board blinks a number of times, pauses, and repeats — two blinks then a pause then two blinks is a "2 flash" code. Watch through at least two full cycles to be sure of the count. A steady, unblinking light is normal; no light at all points at lost power or a failed control. This is a different board from Goodman's modulating furnaces, which show letter codes instead, so confirm your model is one of the ones listed above.
What each code means
Each code carries a safety verdict. Caution means there is a check you can safely make; pro-only means the correct repair is certified work and we do not walk through it here.
No light — No light — lost power or a failed control
No light — lost power or a failed control
A completely dark diagnostic LED means the control board has no power or has failed. Before assuming the board, the common causes are an open furnace disconnect switch, a tripped breaker, or the blower-door safety switch not being pressed in by a properly seated panel.
What you can do: Check the furnace switch (it looks like a light switch nearby), the breaker, and that the blower access panel is seated firmly enough to press its safety switch. If all three are right and the light stays off, the control has likely failed and needs a technician.
1 flash — System lockout — retries or recycles exceeded
System lockout — retries or recycles exceeded
The furnace failed to establish or hold a flame enough times in one call for heat that the control shut the gas off and locked out. It clears itself after about an hour, or when power or the thermostat call is cycled.
What you can do: Confirm the gas is on and the filter is clean, then reset once by lowering the thermostat for several seconds. If it locks out again, stop — repeated lockout is an ignition, gas or flame-sensing fault for a technician.
2 flashes — Pressure switch stuck closed
Pressure switch stuck closed
The control saw the pressure switch already closed before the draft blower started, which should not happen. It points at a stuck switch or its wiring rather than anything a homeowner adjusts.
What you can do: There is no homeowner check here. It is a sealed-switch or wiring diagnosis for a technician.
3 flashes — Pressure switch stuck open
Pressure switch stuck open
After the draft blower started, the pressure switch never closed. The usual causes are a blocked flue or intake pipe, a blocked condensate drain, a weak draft blower, or a failing switch.
What you can do: You can safely check that the outdoor intake and exhaust pipes are clear of snow, leaves or a nest. The drain, the switch and the draft blower are a technician's diagnosis.
4 flashes — Open high limit — usually restricted airflow
Open high limit — usually restricted airflow
The high-limit switch opened because the furnace got too hot, and on this control the most common reason is simply not enough air moving across the heat exchanger.
What you can do: Replace a dirty filter and open any closed or blocked vents — a clogged filter is the leading cause and the one thing you can safely fix. If it returns with a clean filter, the limit or the blower needs a technician.
5 flashes — Flame sensed with no gas valve open
Flame sensed with no gas valve open
The control detected flame when the gas valve should be closed. Because it can indicate a gas valve that is not shutting off fully, it is not a wait-and-see condition.
What you can do: Call a technician. If you also smell gas, leave the house and treat it as the emergency described at the top of this page, not as a code.
6 flashes — Open rollout limit — a combustion safety trip
Open rollout limit — a combustion safety trip
The rollout limit opened, which means burner flames were not being pulled into the heat exchanger properly and rolled back out toward the burner compartment. This is a safety trip, not a nuisance code, and the furnace locks out for a reason.
What you can do: Do not reset this repeatedly to keep the furnace running. A tripped rollout limit points at a blocked heat exchanger, a venting problem or a combustion fault, any of which a qualified technician needs to find before the furnace runs again.
7 flashes — Low flame signal
Low flame signal
The furnace is running but the current the flame sensor reports has fallen below the level the control trusts. It usually means a coated or mispositioned flame sensor, or a weak flame.
What you can do: Cleaning a flame sensor means removing it from the burner assembly, which is combustion work this site does not walk through. It is usually a short, inexpensive technician visit.
Continuous rapid flashing — Reversed 115 VAC polarity
Reversed 115 VAC polarity
The line-voltage hot and neutral are reversed, or the furnace is poorly grounded, and the control will not run until it is corrected. On a newly installed or newly serviced furnace this points back at the wiring.
What you can do: This is line-voltage wiring, for an electrician or the installer. If the furnace was just worked on, it is a callback for whoever wired it.
A note on brand names
We use the Goodman name only to identify which equipment these codes apply to. We are not affiliated with Goodman and are not an official support channel, and the code map above is written in our own words from the published service manual cited below.
Sources (1)
- Goodman Manufacturing — GMS8 / GDS8 / GHS8 Gas-Fired Warm Air Furnace Installation Instructions — Diagnostic Chart (p. 27) and the LED flash-code legend on the wiring diagram (p. 30) (accessed 2026-08-21)