GMSS96

No 120 VAC or no 24 VAC on the IFC. Not a flash code.

1. 1 Measure at the IFC under load

   On Goodman GMSS96 line-voltage codes are incoming power. Measure L1/L2 (or L1/N) at the board while it is trying to run, not just at the disconnect. Door switch, incoming L1/N, transformer, 3 A fuse.

   Expect: Voltage in the rating-plate window under load.

2. 2 Drop, breaker, and the whip

   Large drop from the disconnect to the IFC is a loose lug or damaged whip. Breaker that will not hold under inducer/blower start is the circuit, not the board. If 24 V is present and the LED is dead, IFC.

   Expect: Minimal drop. Tight lugs. Correct breaker size.

3. 3 Transformer 24 V last

   If line is good and 24 V is low, load the transformer (stat + valve + accessories). A collapsing 24 V looks like a comm or fuse call.

   Expect: 24 V holds under load. Line stays in window.

24 V present, no call, no fault. Status.

1. 1 Confirm this is not a fault

   On the Goodman GMSS96 this readout (Steady on) is run status, not a lockout. Write what the display actually shows and whether W/Y/G is present at the IFC.

   Expect: Idle / Ht / CF / stage+CFM words change when you apply and remove the call.

   If fail: If the word never changes on a real call, the call is not reaching this IFC.

   If pass: The board is alive. Diagnose the comfort complaint, not this code.

2. 2 Prove the call at the board

   Measure R to W / Y / G at the Goodman GMSS96 IFC, not at the thermostat. Communicating plates need the data pair and a live indoor address — 24 V on W is not the test.

   Expect: If the house is cold, the call is not reaching W. Check R to W at the IFC, not just at the stat.

   If fail: Fix the stat, harness, or data pair before you change parts.

3. 3 Watch one full sequence

   Leave power on. Watch Single-stage LED IFC through one cycle and write the first real fault that replaces this status word.

   Expect: W: Inducer on → single PS must close → HSI → valve → flame → blower delay.

L1/N swapped. Not ‘code 10’ and not a high flash count.

1. 1 Hot and neutral at the IFC, not the disconnect

   On Goodman GMSS96 polarity/ground is measured at the board. A correctly landed disconnect with a swapped whip at the IFC still throws this. Hot and neutral at the IFC, not just the disconnect.

   Expect: L1 hot, N neutral, ~120 VAC L1 to N, ~0 VAC N to ground.

2. 2 Burner-box and IFC ground

   Green ground to cabinet and IFC. Painted screw and missing star washer fail the ground check and kill flame sense. Burner-box ground. Rapid flash is EA-class, not a PS.

   Expect: Near-zero ohms burner box to IFC ground screw.

3. 3 Then flame and HSI

   Polarity/ground faults take out HSI and flame sense together. After the wiring is right, run one heat cycle and confirm µA and igniter glow before you change those parts.

   Expect: Code cleared. One clean light. µA in range.

Ignition retries exceeded on this call.

1. 1 Watch one full try — do not reset

   Write the Goodman GMSS96 code. Watch inducer, HSI glow, valve click, flame, µA. The step that dies is the repair. Resetting only burns another try into a harder lockout. Watch a try: inducer, HSI, valve, flame.

   Expect: W → No W2 path

2. 2 Gas and the valve

   Cock open, inlet pressure, then manifold on the stage that is failing vs the rating plate. 24 VAC at the valve during trial? Coil ohms? A valve that never opens looks like a ‘bad igniter’ if you did not watch the sequence. Gas, rod, ground. Do not keep resetting.

   Expect: Manifold: Single-stage plate value only — no low/high pair.

3. 3 Flame prove, then the lockout timer

   Glow + valve + no prove → rod, ground, or IFC sense. Prove then drop → µA / PS / limit. Soft lockouts on this family often auto-reset on a long clock — do not sit on resets.

   Expect: Stable µA after light-off. No new PS/limit code.

The single switch is made with the inducer not running.

1. 1 Prove inducer and the live code

   Do not pull power — that clears the Goodman GMSS96 active code. Write 2 flash. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Unplug the PS. Hose water holding residual draft.

   Expect: 120 VAC at the inducer on a heat call. Wheel turning.

   If fail: 120 VAC missing → IFC / door switch / incoming power. Voltage + dead motor → inducer.

   If pass: Inducer running + this code → trap, hose, switch, vent (step 2).

2. 2 Trap, collector, and the hose

   A drowned 96% trap will not make collector pressure. Pull the trap, flush it, confirm the collector box and inducer outlet are not full. Hose cracked, off the port, or full of water fakes an open switch. Welded switch or IFC input shorted.

   Expect: Trap flowing, hose dry and downhill, ports not swapped on a two-switch board.

3. 3 Switch ohms, then vent load

   Ohm the pressure switch: NO, must close when that inducer speed is making the collector setpoint. If the switch is good, walk the PVC — bird screen, ice, long 2" run, wind, shared chase.

   Expect: Single PS: One NO switch. Closed only with inducer up. If you see a second hose hanging, someone mixed this cabinet with a two-stage collector.

   If fail: Replace the open switch only after the vent and trap are proven.

   If pass: Switch closes on draft and the code stays → IFC input.

Draft not proven. The call you will see all winter on 96% Goodman singles.

1. 1 Prove inducer and the live code

   Do not pull power — that clears the Goodman GMSS96 active code. Write 3 flash. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Trap and collector first — these 96%s drown overnight.

   Expect: 120 VAC at the inducer on a heat call. Wheel turning.

   If fail: 120 VAC missing → IFC / door switch / incoming power. Voltage + dead motor → inducer.

   If pass: Inducer running + this code → trap, hose, switch, vent (step 2).

2. 2 Trap, collector, and the hose

   A drowned 96% trap will not make collector pressure. Pull the trap, flush it, confirm the collector box and inducer outlet are not full. Hose cracked, off the port, or full of water fakes an open switch. Inducer 120 VAC and spinning. Hose on the only collector tap.

   Expect: Trap flowing, hose dry and downhill, ports not swapped on a two-switch board.

3. 3 Switch ohms, then vent load

   Ohm the pressure switch: NO, must close when that inducer speed is making the collector setpoint. If the switch is good, walk the PVC — bird screen, ice, long 2" run, wind, shared chase. PVC intake/exhaust, bird screen, ice, wind.

   Expect: Single PS: One NO switch. Closed only with inducer up. If you see a second hose hanging, someone mixed this cabinet with a two-stage collector.

   If fail: Replace the open switch only after the vent and trap are proven.

   If pass: Switch closes on draft and the code stays → IFC input.

Airflow or overfire.

1. 1 Airflow before you touch the limit

   On Goodman GMSS96 a limit is airflow or overfire until proven otherwise. Do not replace the limit first. Filter, blower wheel, A-coil, and the heat-speed setting for THIS motor (tap, model plug, or communicating CFM — not a sister SKU chart). Filter, heat-speed tap, rise, coil.

   Expect: Rise in the rating-plate window. Static vs this cabinet’s blower chart.

2. 2 Measure static and temperature rise

   Total external static vs the Goodman GMSS96 blower chart for this cabinet size. Supply minus return rise after 8–10 minutes. A new 5" media cabinet or closed supplies will trip this all winter. A 96% coil on a furnace left on a low heat tap will limit all season.

   Expect: Rise typically 35–65 °F — rating plate wins.

   If fail: Fix the restriction or the heat-speed setting. The limit is doing its job.

   If pass: Airflow in range → step 3 (overfire / limit itself).

3. 3 Overfire, then the limit circuit

   Clock the meter / manifold on the stage that is tripping vs the rating plate. Then ohm the limit after it cools — a limit that never recloses is failed. Rollout in the same circuit is a different call (see rollout on this door card).

   Expect: Manifold: Single-stage plate value only — no low/high pair.

Leaking valve or false flame sense.

1. 1 Shut the gas cock first

   On Goodman GMSS96 the rod sees flame with the valve de-energized. Shut the cock. If flame stays, the valve is leaking — replace it. Do not jump or energize it as a test. Shut the gas cock. If flame stays, replace the valve.

   Expect: Flame dies when the cock is shut.

   If fail: Leaking valve. Replace. Do not leave the unit.

2. 2 Rod and IFC flame circuit

   If flame dies with the cock shut, the rod is shorted to ground or the IFC flame circuit is lying. Unplug the rod, inspect ceramic, and check the harness for a rub-through on the collector. Rod shorted to ground.

   Expect: Rod isolated from ground. IFC does not report flame with the rod unplugged.

3. 3 Confirm valve solenoids are actually off

   Measure 24 VAC at both solenoids after the call drops. A welded IFC relay or a shorted W will keep a solenoid wet and look like ‘unexpected flame.’ Replace the IFC only after the valve and rod are proven.

   Expect: 0 VAC at both solenoids after the call. No flame.

Manual-reset rollout. Flame containment until proven otherwise.

1. 1 Treat this as flame outside the exchanger

   Do not reset the Goodman GMSS96 rollout and walk away. Write the code, kill the call, and look for flame at the burners, crossover, and vestibule before you do anything else.

   Expect: No flame outside the exchanger. Burners seated. Crossover lit.

   If pass: Still inspect secondary / flue / condensate before you reset.

2. 2 Secondary, condensate, and flue

   Blocked secondary, drowned collector, or a plugged flue pushes flame out the front. Pull the inducer/collector look, confirm the trap is flowing, and check PVC/vent. Exchanger, burners, crossover, flue, secondary / condensate. Reset only after the cause is fixed.

   Expect: Dry collector, open flue, trap clear.

3. 3 Reset only after the cause is fixed

   Manual-reset rollout. Recurring rollout on Goodman GMSS96 is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave.

   Expect: One clean cycle after the cause is fixed. No second reset as a repair.

Weak µA.

1. 1 Measure µA while it is running

   Do not clean first and guess. Series-µA the rod on Goodman GMSS96 during a call. Falling µA is oxide, ground, or a dying flame. A hard drop is often the pressure switch or limit opening, not the rod. Clean rod, chassis ground, manifold, LP conversion.

   Expect: Typically ≥ 1.0 µA DC on this family — confirm the door card. Rising while running.

2. 2 Rod, ground, then gas

   Clean the rod with a non-scratch pad — not sandpaper. Chassis ground to burner box and IFC (painted screw and missing star washer are classic). Then manifold on the stage that is dropping and confirm LP conversion leftovers.

   Expect: Manifold: Single-stage plate value only — no low/high pair.

3. 3 Prove it is not a switch opening

   Watch the live Goodman GMSS96 display when flame drops. A PS or limit code that appears at the drop means the rod was a victim. Inducer, hose, vent wind, or a limit on a wrong heat tap.

   Expect: µA stable and the live code stays a flame code — then rod/valve/IFC. Otherwise chase the new code.

Open / cracked HSI or no 120 VAC during trial.

1. 1 Ohms at the igniter, then at the IFC

   On Goodman GMSS96 measure cold ohms at the igniter plug, then at the IFC connector. An open at the plug is the element or local harness. Open only at the IFC is the harness rub-through on the collector. Ohms at the igniter, then at the IFC.

   Expect: Nitride cold ohms per THIS door sticker — do not use an 80% Norton chart.

2. 2 120 VAC during warm-up

   Call for heat and measure 120 VAC at the igniter during the warm-up window. 0 V + good ohms = IFC igniter relay. Voltage + no glow = cracked nitride. 120 VAC during warm-up. Nitride, not an 80% Norton chart.

   Expect: 120 VAC only during warm-up. Visible glow before the valve opens.

3. 3 Do not keep cycling a cracked element

   A cracked nitride can ohm ‘good’ cold and open hot. If ohms and voltage are good and there is no glow, replace the igniter. Confirm polarity/ground (this plate’s polarity code) before you condemn a new igniter.

   Expect: One clean light after a known-good igniter and a proven ground.

L1/N or chassis ground. Sister to rapid flash on some revisions.

1. 1 Hot and neutral at the IFC, not the disconnect

   On Goodman GMSS96 polarity/ground is measured at the board. A correctly landed disconnect with a swapped whip at the IFC still throws this. Hot/neutral at the IFC.

   Expect: L1 hot, N neutral, ~120 VAC L1 to N, ~0 VAC N to ground.

2. 2 Burner-box and IFC ground

   Green ground to cabinet and IFC. Painted screw and missing star washer fail the ground check and kill flame sense. Burner box to IFC ground screw.

   Expect: Near-zero ohms burner box to IFC ground screw.

3. 3 Then flame and HSI

   Polarity/ground faults take out HSI and flame sense together. After the wiring is right, run one heat cycle and confirm µA and igniter glow before you change those parts.

   Expect: Code cleared. One clean light. µA in range.