N9MSB
ICP / Heil / Tempstar / Comfortmaker Comfort 96 · single-stage · PVC
Heil / Tempstar / Comfortmaker / ICP Comfort 96 single-stage (N9MSB / N9MSE / G9MVE depending on badge). Carrier-platform two-digit IFC. Same 31 / 33 / 34 language as Carrier 59SC5. This slug is the 96% PVC N9MSB — metal-vent 80% cousins exist and are not this trap.
Not Carrier 59TP6 two-stage (dual PS, VS model plug, 32/41/42). Not Goodman GMSS96 flash (1–9 red flashes — 3-flash is not 31). 31 here is Carrier-style two-digit, not Goodman 3-flash.
AFUE
Single-stage 96% condensing · PVC 2-pipe
Staging
Single-stage gas valve · one inducer speed · one pressure switch
Blower
Multi-speed PSC or ECM depending on exact N9MSB / N9MSE SKU — taps, not Infinity ABCD
Control
Carrier-platform two-digit IFC (13/14/24/31/33/34)
Badge
Heil, Tempstar, Comfortmaker, and some G9MVE plates are this IFC
This board
Carrier-platform two-digit IFC
- Codes are two digits: 13, 14, 24, 31, 33, 34. They flash as tens then ones, same language as Carrier 59SC5.
- 31 is draft / pressure switch on this single-stage 96%. There is no second high-fire PS and no 32 low-fire twin like 59TP6.
- 33 is limit / rollout circuit. Three minutes of 33 becomes lockout 13 (~3-hour auto reset).
- 34 is ignition prove fail. Repeats become lockout 14.
- Do not count these as Goodman flashes. A house with a Goodman 3-flash and an ICP 31 in the same mechanical room is two different parents.
Last codes store until power is pulled (11 = no history). Use the diagnostic button where equipped. Write the two-digit code before you cycle power.
Universal swap
Carrier-platform Comfort 96. Same HK42FZ / CES rule as 59SC5. ICM282B or 50M56U when the silk matches.
Silk: HK42FZ004 · HK42FZ007 · HK42FZ008 · HK42FZ009 · HK42FZ011 · HK42FZ013 · HK42FZ016 · HK42FZ034 · CES0110057 · 1010806 · 1380686
White-Rodgers
- 50M56U-843
HK42FZ004/007/008/009/011/016 — not 013.
Honeywell
- S9200U1000
Resideo lists ICP 1010806 / 1380686 and 50A55-843. Not an HK42FZ drop-in — photograph the silk.
- Infinity boards. 59TP6 VS two-stage. 50A55 onto a motor this board did not ship with.
After you pull the dead card
- 1Kill power. Photograph the silk-screen part number on the dead board before you pull it.
- 2Match staging (1 vs 2 vs modulating), igniter (carbide / nitride / spark), and motor (PSC / ECMx / 9-speed tap / serial VS).
- 3Set heat-off delay and any 80+/90+ jumper to the door card. Prove one full try and flame µA before you leave.
Field wiring
Written landings for ICP N9MSB. Not a factory schematic.
Conventional single-stage furnace IFC. One W. Cool Y passes through to the outdoor. No ComfortBridge, no ABCD, no W2.
Written circuit description only — FieldBench does not redraw maker schematics. Example: R to W closes on a heat call; verify 24V at W1 before you change the IFC.
Open manufacturer PDFHeat sequence
- 1Power. L1 / N → IFC → transformer → R120V in, 24V out
- 2Call. Stat W → IFC W~24 VAC
- 3Draft. IFC → inducer → PS close120V motor, 24V prove
- 4Ignite. IFC → HSI120 VAC
- 5Gas. IFC → valve~24 VAC
- 6Flame. Rod → IFCµA DC
- 7Blow. IFC → heat speedAfter flame prove
This indoor
ICP Comfort 96 PSC. Carrier-platform 24V.
24V single-stage heat
Door card is one-stage. Twin terminal empty unless the job is actually twinned.
Wall thermostat
Single-stage heat/cool. W2 from a leftover two-stage stat does nothing useful.
- R24V hot from the IFC24V
- CCommon24V
- WHeat24V
- YCool — also starts the outdoor24V
- GFan24V
Furnace IFC
Transformer lives here. Y out to the outdoor contactor. TWIN empty on a standalone.
- RHot to the stat24V
- CCommon — must reach the outdoor24V
- WHeat call24V
- YCool in / cool out24V
- GBlower24V
- TWINEmpty unless twinned24V
Landing
- 24VIFC Rstat R
~24 VAC hot
- 24VIFC Cstat Coutdoor C
Common
- 24VStat WIFC W
Heat. Stays in this cabinet.
- 24VStat YIFC Youtdoor Y
Cool / contactor
- 24VStat GIFC G
Fan. Does not go outdoors.
IFC harness — single-stage heat
After W arrives. This is the gas train, not the thermostat strip.
Transformer + fuse
120V primary. 24V secondary. Dark stat = fuse / door / transformer first.
- L1 / N120V to the IFCLine
- XFMR24V to R24V
- FUSEOn the IFC24V
24V safety chain
Door, limit, rollout in series. Open anywhere kills heat.
- DOORInterlock24V
- LIMITMain limit — rise / no airflow24V
- ROLLOUTManual reset. Do not jumper and leave24V
Inducer + one pressure switch
W → inducer 120V → PS closes → IFC continues. One hose, one switch.
- IND120V from the IFC to the inducerLine
- PS24V prove back to the IFC24V
- HOSESingle hose. Do not add a second because two-stage boards have two.24V
HSI + single valve
Igniter is 120V from the IFC. Valve is 24V. Flame rod is µA DC back to the IFC.
- HSI120V hot-surface igniter — not 24VLine
- VALVE24V to the single solenoid24V
- FLAMEµA DC on the rod. Not a 24V circuit24V
PSC blower + run cap
Heat / cool / park taps on the motor. The cap is on this blower — not the outdoor dual can.
- HEATHeat speed tap24V
- COOLCool speed tap24V
- PARKUnused leads parked24V
- CAPRun capacitor on the blowerCap
Landing
- LineL1IFCinducer
120 VAC after W
- 24VIFCPSIFC
~24 VAC prove. Open PS = no ignition.
- LineIFCHSI
120 VAC during trial
- 24VIFCgas valve
~24 VAC after flame prove starts
- 24VFlame rodIFC
µA DC. Not 24V.
- LineIFCblower
120V tap + cap
Prove it
- 24 VAC from R to C at the IFC. Fuse / transformer first if the stat is dark.
- W at the IFC under a heat call. Then inducer / igniter / valve per THIS door card.
Do not
- Do not land a ComfortBridge 1/2 or Infinity ABCD pair on this IFC.
- Do not hunt W2 / E8 / high-fire on a one-stage door.
- TWIN must be empty on a standalone.
9-speed tap, PSC, and CT motors share this thermostat landing. The motor is on the IFC harness diagram.
Sequence
- 1
W
Inducer on → the single PS must close (31 if it will not) → HSI → valve → flame (34 if no prove) → blower on the heat tap.
- 2
No W2 path
Single-stage. A leftover W2 from a previous two-stage furnace does nothing useful here.
- 3
Limits
33 live, then 13 lockout if it stays open. Rollout is on the same circuit — inspect before you reset.
Faults on this IFC
Step 1, then 2, then 3. Expected reading and the fail branch sit under each check.
11
No stored history
Memory empty or power was cycled.
1 Confirm this is not a fault
On the ICP N9MSB this readout (11) 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 Prove the call at the board
Measure R to W / Y / G at the ICP N9MSB 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: Not a fault. Recreate the call and watch the live code.
If fail: Fix the stat, harness, or data pair before you change parts.
3 Watch one full sequence
Leave power on. Watch Carrier-platform two-digit IFC through one cycle and write the first real fault that replaces this status word.
Expect: W: Inducer on → the single PS must close (31 if it will not) → HSI → valve → flame (34 if no prove) → blower on the heat tap.
12
Blower on after power-up
Powered up on a W call — blower runs ~90 s.
1 Confirm this is not a fault
On the ICP N9MSB this readout (12) 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 Prove the call at the board
Measure R to W / Y / G at the ICP N9MSB 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: Normal after a brownout. Repeating 12 with a limit complaint → airflow, not a bad 12.
If fail: Fix the stat, harness, or data pair before you change parts.
3 Watch one full sequence
Leave power on. Watch Carrier-platform two-digit IFC through one cycle and write the first real fault that replaces this status word.
Expect: W: Inducer on → the single PS must close (31 if it will not) → HSI → valve → flame (34 if no prove) → blower on the heat tap.
13
Limit lockout
Limit/rollout stayed open. Auto-reset ~3 h. Hardened 33.
1 Treat this as flame outside the exchanger
Do not reset the ICP N9MSB 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 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. Treat as a 33 that won. Filter, heat tap, coil, return, rollout reset. Do not sit on 3-hour resets.
Expect: Dry collector, open flue, trap clear.
3 Reset only after the cause is fixed
Manual-reset rollout. Recurring rollout on ICP N9MSB 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.
14
Ignition lockout
Hardened 34. Auto-reset ~3 h.
1 Watch one full try — do not reset
Write the ICP N9MSB 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. HSI, gas, flame sensor, ground. Same prove path as 59SC5.
Expect: W → No W2 path → Limits
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.
Expect: Inlet and manifold on the plate. 24 VAC only during trial.
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.
22
Flame with valve off
Flame sense while the gas valve is de-energized.
1 Shut the gas cock first
On ICP N9MSB 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. Leaking valve. Shut the cock.
Expect: Flame dies when the cock is shut.
If fail: Leaking valve. Replace. Do not leave the unit.
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.
Expect: Rod isolated from ground. IFC does not report flame with the rod unplugged.
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.
24
Secondary fuse open
24 V fuse on the IFC.
1 Find the 24 V short before you replace the fuse
On ICP N9MSB 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. Tstat short, HUM/EAC, valve harness. Replace the fuse only after the short is gone.
Expect: Fuse out. 24 V transformer still good. Harness isolated.
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).
Expect: Fuse holds with harness off. Dies when the shorted lead lands.
3 If it blows with the harness off
Short is on the ICP N9MSB 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.
31
Draft / pressure switch
Inducer running, the one PS did not close (or the draft path will not hold). On this 96% that is trap / PVC / inducer.
1 Prove inducer and the live code
Do not pull power — that clears the ICP N9MSB active code. Write 31. Is the inducer spinning on this call? Silent inducer is not a pressure switch. One PS only — do not hunt a second high-fire switch.
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 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. Dump the trap and open the collector. N9MSB 96% drowns overnight.
Expect: Trap flowing, hose dry and downhill, ports not swapped on a two-switch board.
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, ice, wind, hose on the only collector tap.
Expect: Pressure switch: One NO switch. Closed only with the inducer up. No second hose.
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.
33
Limit or rollout open
The winter callback. Airflow first; rollout is hazard.
1 Treat this as flame outside the exchanger
Do not reset the ICP N9MSB 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 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. Filter, heat-speed tap (this is not a VS 59TP6 menu), coil, return, TES. Rise vs plate. Overfire on a single-stage orifice.
Expect: Dry collector, open flue, trap clear.
3 Reset only after the cause is fixed
Manual-reset rollout. Recurring rollout on ICP N9MSB is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave. Rollout manual reset — inspect exchanger / burners / flue before you reset.
Expect: One clean cycle after the cause is fixed. No second reset as a repair.
34
Ignition prove fail
Trial without flame sense. Repeats → 14.
1 Measure µA while it is running
Do not clean first and guess. Series-µA the rod on ICP N9MSB 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. HSI glow and 120 VAC, gas cock, manifold, flame rod, IFC ground.
Expect: Typically ≥ 1.0 µA DC on this family — confirm the door card. Rising while running.
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. If 31 is also stored, fix draft first or you will never get a fair 34.
Expect: Manifold on the rating plate. Solid burner-box ground.
3 Prove it is not a switch opening
Watch the live ICP N9MSB 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.
Workflows
33 on ICP 96%
Heat starts, then drops. 33 live or 13 lockout.
1 Prove the call and the live code
Two-digit 33, not Goodman 4-flash and not York 4-red. Same meaning as Carrier 59SC5.
Expect: Write whatever Carrier-platform two-digit IFC is showing. Last codes store until power is pulled (11 = no history). Use the diagnostic button where equipped. Write the two-digit code before you cycle power.
If fail: No call at the IFC → stat / harness. Do not change gas parts.
2 Isolate the first failed step in the sequence
Heat tap on this multi-speed motor vs the N9MSB chart and the rise range. There is no 59TP6 model-plug CFM menu.
Expect: No W2 path: Single-stage. A leftover W2 from a previous two-stage furnace does nothing useful here.
3 Confirm with a number, then the next part
Filter, coil, return. Media cabinets trip 33 all winter. Walk the rollout on the same circuit before you leave. Resetting a rollout without an inspection is a CO call.
Expect: Display: Two digits. 31 ≠ Goodman 3-flash. 33 ≠ York 4-red. · Pressure switch: One NO switch. Closed only with the inducer up. No second hose.
If fail: Stay on this plate. The out-of-range reading is the part.
If pass: Reading in range → the next step in this workflow is the repair.
31 trap / PVC
Inducer runs, no light-off, display 31.
1 Prove the call and the live code
Single-stage 96% — one PS, one hose, PVC, trap. Not a metal-vent 80% cousin.
Expect: Write whatever Carrier-platform two-digit IFC is showing. Last codes store until power is pulled (11 = no history). Use the diagnostic button where equipped. Write the two-digit code before you cycle power.
If fail: No call at the IFC → stat / harness. Do not change gas parts.
2 Isolate the first failed step in the sequence
Dump the trap and the collector first.
Expect: No W2 path: Single-stage. A leftover W2 from a previous two-stage furnace does nothing useful here.
3 Confirm with a number, then the next part
Then inducer, hose, termination ice/wind. If the PS closes and 31 remains, the IFC input is the fault.
Expect: Display: Two digits. 31 ≠ Goodman 3-flash. 33 ≠ York 4-red. · Pressure switch: One NO switch. Closed only with the inducer up. No second hose.
If fail: Stay on this plate. The out-of-range reading is the part.
If pass: Reading in range → the next step in this workflow is the repair.
Identify vs Goodman 3-flash
The house has both an ICP and a Goodman, or the last invoice says ‘code 3.’
1 Prove the call and the live code
ICP N9MSB / Heil / Tempstar: two-digit display. 31 is draft. 33 is limit. 34 is ignition.
Expect: Write whatever Carrier-platform two-digit IFC is showing. Last codes store until power is pulled (11 = no history). Use the diagnostic button where equipped. Write the two-digit code before you cycle power.
If fail: No call at the IFC → stat / harness. Do not change gas parts.
2 Isolate the first failed step in the sequence
Goodman GMSS96: red LED flash counts. 3-flash is PS open. 4-flash is limit. Different parent, different board.
Expect: No W2 path: Single-stage. A leftover W2 from a previous two-stage furnace does nothing useful here.
3 Confirm with a number, then the next part
Do not pull a Goodman 3-flash video onto this IFC. Do not pull this 31 onto the Goodman. 59TP6 in the same house is two-stage Carrier with extra codes (32/41/42) this single-stage N9MSB does not use.
Expect: Display: Two digits. 31 ≠ Goodman 3-flash. 33 ≠ York 4-red. · Pressure switch: One NO switch. Closed only with the inducer up. No second hose.
If fail: Stay on this plate. The out-of-range reading is the part.
If pass: Reading in range → the next step in this workflow is the repair.
Test points
Display
Two digits. 31 ≠ Goodman 3-flash. 33 ≠ York 4-red.
Pressure switch
One NO switch. Closed only with the inducer up. No second hose.
Fuse
24 V secondary fuse. 24 = open fuse, not a draft code.
Gotchas
- G9MVE and N9MSE badges are this Comfort 96 IFC when the plate is 96% PVC single-stage. An 80% metal-vent ICP with the same two-digit look is not a trap call.
- 59TP6 two-stage codes (32, 41, 42, model plug) do not belong on N9MSB.
- A leftover W2 wire from a previous furnace is a decoy.
Related plates
Install this plate
Install N9MSB as ICP / Heil / Tempstar Comfort 96. Carrier-platform 31/33/34. One PS.
Cat IV PVC · single-stage · one PS · PSC or ECM taps (N9MSB / N9MSE) · two-digit 13/14/24/31/33/34
IFC & vent
- Same 31/33/34 language as Carrier 59SC5. 31 is PVC / trap / inducer — not Goodman 3-flash.
- N9MSB PSC vs N9MSE ECM — taps, not Infinity ABCD.
- Use 44001410103 plus the door card on THIS revision. Some later 96% ICP plates supersede the 2012 92.1% I/O lengths.
First fire
- 1W: 31 close, 34 ignition, heat tap. Cap W2.
- 2Rise vs the N9MSB / N9MSE chart for this cabinet.
Do not on ICP N9MSB
- Do not apply 59TP6 dual-PS / model-plug setup.
- Do not count Goodman 1–9 flashes on this two-digit IFC.
Maker literature
FieldBench does not host manufacturer files. Each link opens the maker’s own literature page in a new tab.
- N9MSB installation instructions (44001410103)Maker installICP I/O for N9MSB 92.1% single-stage PSC. Later N9MSB/N9MSE 96% revisions share the two-digit IFC — confirm the door card.Open manufacturer PDF
- ICP commercial literatureLiterature searchHeil / Tempstar / Comfortmaker / ICP N9MSB I/O and owner PDFs.Open manufacturer PDF
- Tempstar / ICP gas furnacesProduct pageHeil, Tempstar, Comfortmaker badges share this Carrier-platform Comfort 96 IFC.Open manufacturer PDF
Warranty and bulletins
Affected models, serial range, symptom, remedy, date. Maker files open on the manufacturer site.
Residential limited warranty
warranty sheetICP / Heil / Tempstar / Comfortmaker furnace warranty
Registered Comfort 96 / 80 furnace warranty · Distributor claim path
Dealer portals
dealerWhere remaining service letters live
Current-year service letters not on a public literature page · Maker dealer portal