8 components coveredField manual · Furnace
Goodman / Amana 80% single-stage gas furnaces (GMS8, GMH8, GM9S80, GC9S80): quick sheet
Covers: Goodman and Amana non-condensing (80%) single-stage furnaces with a single red or green diagnostic LED: GMS8 / GMH8 (older), GM9S80 / GC9S80 (current) and Amana/Daikin badged equivalents. For the 96% GM9S96 / GMVC96 see the separate condensing quick sheet.
The most common builder-grade 80% furnace in the US. The integrated control board flashes a single LED in groups; count the flashes through the sight glass with power on. Power-off clears the code. Because it is 80% (non-condensing), there is no condensate trap; pressure-switch faults point to the inducer, hose, switch or the metal vent.
Safety first
- Gas valve, burners, heat exchanger and venting are blocked: refer to a licensed HVAC/gas technician.
- Read the code before cutting power; then lock out 120 V.
- 6 flashes (rollout) is a CO risk: shut down and refer; do not bypass or keep resetting.
How it works
Sequence of operation on a W call: the board confirms the pressure switch is open, energizes the inducer, waits for the pressure switch to close, runs a pre-purge, heats the hot surface igniter, then opens the gas valve for the trial for ignition. Flame must be proven by the flame sensor or the board retries.
After a fixed heat-on delay the circulator starts at heat speed. At the end of the call the valve closes, the inducer post-purges and the blower runs the selectable heat-off delay.
The board watches the high limit and rollout circuit continuously. A high limit trip is automatic-reset once the furnace cools; rollout switches on these furnaces are manual-reset and indicate a serious combustion problem.
After repeated failed ignitions the board goes into lockout (1 flash). Lockout typically clears after a timed period or by cycling the thermostat or power, but the cause must be found first.
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OnCall Tech is a reference tool for trained technicians and can make mistakes. Always disconnect power and confirm with the manufacturer's documentation before you work. © 2026 OnCall Tech. Original content; not a reproduction of any manufacturer document.Generic part photos (not of this brand): Ductless mini-split indoor head mounted high on a wall by NEOSiAM, Pexels License
