GR9T80

Too many failed ignition attempts or flame losses on this call.

1. 1 Measure µA while it is running

   Do not clean first and guess. Series-µA the rod on Goodman GR9T80 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. Watch one full try: inducer, HSI glow, valve click, flame, µA.

   Expect: Flame rod: Typically ≥ 1.0 µA DC on this IFC family — confirm door chart. Rising while running is the goal.

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. Gas supply and manifold (low then high).

   Expect: Manifold low / high: Natural ~1.6–1.9 / 3.2–3.5 in. w.c. class — rating plate wins. Clock input if in doubt.

3. 3 Prove it is not a switch opening

   Watch the live Goodman GR9T80 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. Ground and flame-rod cleanliness.

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

Low-stage pressure switch is made with the inducer off.

1. 1 Unplug the switch with the inducer off

   On Goodman GR9T80 this code is the switch made when the inducer is not running. Unplug that switch only. This is Category I metal vent. There is no 96% collector or PVC trap to prime.

   Expect: Code changes when the harness is open.

   If fail: Wrong switch, or the IFC input is shorted.

   If pass: Switch/hose path. Go to step 2.

2. 2 Water in the hose vs a welded switch

   Blow the hose. Water holding residual draft is more common than a welded switch. Confirm the hose is not teed and not routed uphill. Ohm the switch with the hose off. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   Expect: Hose empty. Switch opens with no draft.

3. 3 IFC input last

   If the switch ohms open, the hose is dry, and the code does not change with the harness off, the Goodman GR9T80 IFC input is shorted. Do not keep swapping switches. Unplug the LPS. If code changes, switch is welded or hose is holding residual draft.

   Expect: Known-good open switch + open harness = code gone. If not, IFC.

Inducer is on low and the low-fire switch will not close.

1. 1 Prove inducer and the live code

   Do not pull power — that clears the Goodman GR9T80 active code. Write E2. Is the inducer spinning on this call? Silent inducer is not a pressure switch. This is Category I metal vent. There is no 96% collector or PVC trap to prime.

   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. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   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. Inducer spinning? 120 VAC at inducer on a W1 call.

   Expect: LPS / HPS: Both NO. Closed only when that inducer speed is making the collector setpoint. Two hoses — never tee.

   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.

Primary limit opened. Airflow or overfire — not a charge problem.

1. 1 Airflow before you touch the limit

   On Goodman GR9T80 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, blower wheel, A-coil, heat-speed tap (9-speed: wrong tap is the #1 callback).

   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 GR9T80 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. Static vs blower chart for this cabinet size.

   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). Manifold pressure on low and high vs rating plate.

   Expect: Manifold low / high: Natural ~1.6–1.9 / 3.2–3.5 in. w.c. class — rating plate wins. Clock input if in doubt.

Rod sees flame with both solenoids de-energized.

1. 1 Shut the gas cock first

   On Goodman GR9T80 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, leaking valve — replace, do not jump.

   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 or IFC flame circuit.

   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.

3 A (typical) automotive fuse on the IFC is open.

1. 1 Find the 24 V short before you replace the fuse

   On Goodman GR9T80 an open IFC fuse is a short on W, Y, G, HUM, EAC, or a data pair landed on 24 V. Unplug the thermostat / data harness first. 24 V short on W, Y, G, humidifier, or EAC.

   Expect: Fuse out. 24 V transformer still good. Harness isolated.

2. 2 Replace the fuse with the harness off

   New fuse, harness still off. If it holds, the short is in the field wiring or accessory. Plug one circuit back at a time (W, then Y, then HUM/EAC). Unplug tstat harness and replace fuse. If it blows again the short is on the board or gas valve harness.

   Expect: Fuse holds with harness off. Dies when the shorted lead lands.

3. 3 If it blows with the harness off

   Short is on the Goodman GR9T80 IFC or the gas-valve harness. Unplug the valve and try once more. Repeat blow with valve unplugged = IFC.

   Expect: Do not keep feeding fuses into a welded valve coil or a burned IFC trace.

Flame is present but µA is below the IFC threshold.

1. 1 Measure µA while it is running

   Do not clean first and guess. Series-µA the rod on Goodman GR9T80 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 with a non-scratch pad — not sandpaper.

   Expect: Flame rod: Typically ≥ 1.0 µA DC on this IFC family — confirm door chart. Rising while running is the goal.

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. Chassis ground to burner box and IFC.

   Expect: Manifold low / high: Natural ~1.6–1.9 / 3.2–3.5 in. w.c. class — rating plate wins. Clock input if in doubt.

3. 3 Prove it is not a switch opening

   Watch the live Goodman GR9T80 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. Manifold pressure / orifice / LP conversion.

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

IFC did not see the igniter circuit behave as commanded.

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

   On Goodman GR9T80 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. Igniter ohms cold (OEM — typically 30–115 Ω class, confirm sticker).

   Expect: HSI: Nitride, 120 VAC during warm-up. Cold ohms per sticker — do not use a 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 to igniter during warm-up.

   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. Cracked nitride element.

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

High-stage pressure switch is made with the inducer not on high.

1. 1 Prove the switch is made with inducer not on high

   On Goodman GR9T80 this code means the high-fire switch is closed when it should be open. Do not treat it as the low-fire stuck-closed code. Write the live display, then unplug the high-fire switch only.

   Expect: Code should change when the high-fire harness is open.

   If fail: IFC input shorted or you unplugged the wrong switch.

2. 2 Hose water and a welded switch

   Water in the high-fire hose holds residual draft and fakes a closed switch. Route downhill to the collector. Ohm the switch with the hose off — a welded high-fire switch stays closed. This is Category I metal vent. There is no 96% collector or PVC trap to prime. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   Expect: Hose dry. Switch opens with no draft.

3. 3 Confirm the IFC is not commanding high

   W2 shorted to W1, a communicating stat stuck on high, or an IFC that never drops inducer speed will keep this code alive. Measure W2 at the board and watch inducer speed after you open the high-fire harness. This is the second switch — do not confuse with E1.

   Expect: Inducer on low (or off) with W2 open. High-fire switch ohms open.

Inducer on high, high-fire switch never closes. Classic ‘runs on low, will not go high.’

1. 1 Prove the high-fire call

   Write the live Goodman GR9T80 code before you pull power. Confirm this IFC is actually commanded to high — W2 at the board, or the staging timer has expired. This is Category I metal vent. There is no 96% collector or PVC trap to prime.

   Expect: R to W2 ~24 VAC (conventional) or a high-stage request on a communicating stat.

   If fail: No high request → thermostat / staging / menu. Not a high-fire pressure switch.

   If pass: Go to step 2. Do not jump the high-fire switch to ‘see if it runs.’

2. 2 Prove the inducer actually went high

   Listen and amp the inducer on low vs high. No speed-up → IFC high output or inducer winding. Speed-up and this code still live → high-fire PS path (hose, switch, vent). Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   Expect: LPS / HPS: Both NO. Closed only when that inducer speed is making the collector setpoint. Two hoses — never tee.

   If fail: Measure 120 VAC on the high-speed inducer lead during the high call. 0 V = IFC. Voltage + dead motor = inducer.

3. 3 Isolate the HIGH hose and switch

   High-fire hose on the high tap only — a tee with the low switch is the common first-install miss on this dual-switch plate. Blow the hose, confirm it is dry and downhill to the collector. Ohm the high-fire switch: it is NO and must close only on high draft. Inducer actually changes speed on W2? Listen / amp it.

   Expect: LPS / HPS: Both NO. Closed only when that inducer speed is making the collector setpoint. Two hoses — never tee.

   If fail: Welded open, cracked hose, or water in the line. Replace the failed part — do not leave a jumper.

   If pass: Switch and hose good → step 4 (vent / condensate / IFC).

4. 4 Vent, condensate, and the IFC input

   High fire needs more draft than a low-fire code ever saw. Check PVC size on this cabinet, shared chase, wind, ice, bird screen, and condensate backing into the collector only on high. If the switch closes on known draft and the code stays, the Goodman GR9T80 IFC input is the last call.

   Expect: Clear vent, dry collector, known-good switch, then IFC.

L1/N reversed or chassis ground missing. HSI and flame sense both suffer.

1. 1 Measure µA while it is running

   Do not clean first and guess. Series-µA the rod on Goodman GR9T80 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. Hot and neutral at the IFC, not just the disconnect.

   Expect: Flame rod: Typically ≥ 1.0 µA DC on this IFC family — confirm door chart. Rising while running is the goal.

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. Burner box to IFC ground screw.

   Expect: Manifold low / high: Natural ~1.6–1.9 / 3.2–3.5 in. w.c. class — rating plate wins. Clock input if in doubt.

3. 3 Prove it is not a switch opening

   Watch the live Goodman GR9T80 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. Twinned jobs — follow the twinning kit, then look at EEJ.

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

Internal (Eb) or external (Ec) gas-valve electrical fault.

1. 1 Coil ohms and 24 VAC during trial only

   On Goodman GR9T80 measure each solenoid. 24 VAC should appear only during trial / the commanded stage. Valve coil ohms, 24 VAC at the harness during trial.

   Expect: Coil ohms per the valve sticker. 24 VAC only when the IFC commands that stage.

2. 2 Do not energize a leaking valve

   If the unexpected-flame code is also in history, shut the cock and replace the valve. Applying 24 V as a ‘test’ and walking away is a gas leak. Do not apply 24 V to a leaking valve as a ‘test’ and walk away.

   Expect: No flame with the cock shut and solenoids de-energized.

3. 3 IFC relay vs the valve

   Voltage at the harness and a dead coil = valve. No voltage during a known trial = IFC relay or a lockout that never opened the valve (look at the live code).

   Expect: Known trial + 24 VAC + good coil = flame. Otherwise IFC.

Manual-reset rollout opened. Treat as flame outside the exchanger until proven otherwise. Door chart may render this as a distinctive 7-seg character — confirm on the unit sticker.

1. 1 Treat this as flame outside the exchanger

   Do not reset the Goodman GR9T80 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. Primary exchanger cracks, burner alignment, crossover. Blocked secondary / condensate / flue.

   Expect: Dry collector, open flue, trap clear.

3. 3 Reset only after the cause is fixed

   Manual-reset rollout. Recurring rollout on Goodman GR9T80 is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave. Reset only after the cause is fixed. Recurring rollout is a CO / fire call.

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

Igniter circuit measures open.

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

   On Goodman GR9T80 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 plug, then at the IFC.

   Expect: HSI: Nitride, 120 VAC during warm-up. Cold ohms per sticker — do not use a 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. Harness rub-through on the collector.

   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.

IFC failed its ground check (sister to EA).

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

   On Goodman GR9T80 polarity/ground is measured at the board. A correctly landed disconnect with a swapped whip at the IFC still throws this. Green ground to cabinet and 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. Painted screw, missing star washer.

   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.

Twinning miswire or twin terminal active on a standalone unit.

1. 1 Is this cabinet actually twinned?

   On a standalone Goodman GR9T80, nothing belongs on the TWIN terminal. A leftover jumper throws this. If not twinned, nothing should be on the TWIN terminal.

   Expect: TWIN empty on a single cabinet.

2. 2 Twinned pair must be the same IFC family

   Twinned units must be the same family and IFC revision. Mixing this plate with a communicating sister SKU will not twin. Twinned pair must be same family / same IFC revision.

   Expect: Same model family, same IFC, kit installed per the twinning sheet.

3. 3 Phasing and 24 V

   Twinning errors that survive a correct kit are 24 V phasing or a broken twin lead. Measure both cabinets before you change an IFC.

   Expect: In-phase 24 V. Continuous twin lead.

ECM current too low (LE1) or unexpected (UE2).

1. 1 Is the wheel free?

   Spin the Goodman GR9T80 blower by hand. Ice, debris, or a seized bearing is not a control problem. Confirm the motor type on this plate — serial ECM, 9-speed tap, or X-13 — before you grab a capacitor. This is Category I metal vent. There is no 96% collector or PVC trap to prime.

   Expect: Wheel free. Correct motor family for this IFC.

2. 2 Command vs rotation

   Call for G or heat and confirm the IFC is actually requesting CFM (taps, serial, or communicating). Amp the motor. Locked rotor + a good command = motor. No command = IFC / harness / shared data. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   Expect: ECM taps: Factory defaults from SS p.8: fan F03, Y1/Y F04, Y2 F05, heat low F01, heat high F02. Rise is cabinet-specific (15–45 on 0303AN through 35–65 on 80–120 kBtu).

3. 3 Static and the wrong motor

   High static will trip current/limit codes and look like a dead motor. Measure TES vs this cabinet. Wrong horsepower or a leftover memory card after a control swap is the other half of this call. Harness seated at motor and IFC. 9-speed ECM is tap-driven — a half-seated plug throws these.

   Expect: Static on the blower chart. Matching motor / shared-data card.

Leak / comm / relay alarm from the A2L board when paired with R-32 or R-454B outdoor.

1. 1 Confirm this pair is actually A2L

   On Goodman GR9T80 FE3 / LE4 / SE5 / rE6-class codes are only valid when this furnace is tied to an R-32 or R-454B outdoor. On R-410A this is a miswired mitigation harness — not a leaking indoor coil.

   Expect: Outdoor refrigerant from the outdoor nameplate, not from memory.

   If fail: Remove / correct the mitigation harness. Do not condemn the IFC.

2. 2 Sensor location and the mitigation blower

   If it is a real A2L pair, follow the OEM mitigation sequence: sensor location, ventilation blower, relay. This is Category I metal vent. There is no 96% collector or PVC trap to prime. Cap, liner, common-vent tables, inducer wheel, hose on the inducer housing.

   Expect: Sensor seated where the I/O shows. Mitigation blower runs on a test.

3. 3 Do not bypass mitigation

   Never jump an A2L alarm to get heat. Find the leak or the failed sensor. Recurring mitigation with a clean sensor is a refrigerant leak until proven otherwise.

   Expect: Alarm clears only after the leak/sensor is fixed.