Carrierfurnace

58STA

Comfort 80 · single-stage · Category I metal vent

Carrier Comfort 80% single-stage Category I metal-vent furnace. 58STA / 58STX are the single-stage Comfort 80. 58CTA is the two-stage 80% cousin (same vent physics, extra solenoid / high-fire path). Older and current boards speak two-digit codes or a vintage LED-status chart — 31 is always metal-vent draft / inducer / common vent, never a PVC condensate trap.

Not 58CVA / 58MVC Infinity 80 (ABCD communicating two-stage). Not 59SC5 Comfort 96 (PVC trap — a 31 there is a collector, not a chimney). 58CTA is the two-stage 80% cousin: same 31 metal-vent meaning, but it has W2 / high fire this single-stage STA does not.

Diagnose this model Install notes Board cross-ref Field wiring

AFUE

80% class · Category I

Staging

58STA/58STX: single-stage gas, one draft switch. 58CTA cousin: two-stage 80%

Vent

Metal chimney / Type B — not PVC, no secondary collector

Control

Conventional 24V. Two-digit IFC or older LED-status depending on vintage

Sister

58STX, 58DL older Deluxe 80, 58CTA two-stage Comfort 80

This board

Two-digit or vintage LED-status IFC (Comfort 80)

Current boards use Carrier two-digit: 11–14, 21–24, 31, 33, 34.
Older Comfort 80 IFCs use an amber LED status chart on the door. Do not import two-digit meanings onto a 1–6 flash board without that sticker, and do not import an old flash chart onto a two-digit display.
31 = metal-vent draft / inducer / common vent. NEVER a PVC condensate trap.
No 32 low-fire code on single-stage STA. If you are looking at 32, you are on a two-stage board (58CTA / 59TP6 / 59TN6) or the wrong card.

Two-digit: last codes ~48 h or until power is pulled (11 = no history). LED vintage: flashes until power is pulled — write the count against THIS door card.

Universal swap

Read the silk

Classic Comfort 80. ICM282B or 50M56U on HK42FZ004–016/034. Very old CES011 → ICM281.

Silk: HK42FZ004 · HK42FZ007 · HK42FZ008 · HK42FZ009 · HK42FZ011 · HK42FZ013 · HK42FZ016 · HK42FZ034 · CES0110020

White-Rodgers

50M56U-843
HK42FZ004/007/008/009/011/016 — not 013.
50A55-843
If the silk is already a 50A50 / 50A55.

ICM

ICM282B
HK42FZ004–016/034 including 013.
ICM281
CES0110020 / 0048 / 0057 only.

Honeywell

S9200U1000
Only if the silk is already a 50A50 / 50A55. S9200U does not list HK42FZ — that stays ICM282B.

58CVA Infinity two-stage. 59SC5 96% board without checking vent and silk.

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.
4Cat I metal vent. Prove draft. Do not hang a 96% condensing board in this cabinet.

Field wiring

Written landings for Carrier 58STA. Not a factory schematic.

Furnace · single-stage 24V

R / C / W / Y / GGas furnace

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 PDF

Heat 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

Comfort 80. Same 24V. Metal vent.

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 → metal-vent draft switch must close (31 if not) → HSI → single-stage valve → flame (34 if no prove) → heat-speed blower.
2
No PVC
Category I. There is no collector and no trap to dump. 31 lives in the chimney, cap, liner, common vent, and inducer wheel.
3
58CTA cousin
Two-stage 80% adds W2 and a high-fire path. Still metal vent. Still not a 96% trap. Do not use that high-fire path on an STA.

Faults on this IFC

Step 1, then 2, then 3. Expected reading and the fail branch sit under each check.

No stored history

info

Memory empty or power was cycled (two-digit boards).

1 Confirm this is not a fault
On the Carrier 58STA 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 Carrier 58STA 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 W call.
If fail: Fix the stat, harness, or data pair before you change parts.
3 Watch one full sequence
Leave power on. Watch Two-digit or vintage LED-status IFC (Comfort 80) through one cycle and write the first real fault that replaces this status word.
Expect: W: Inducer → metal-vent draft switch must close (31 if not) → HSI → single-stage valve → flame (34 if no prove) → heat-speed blower.

Blower on after power-up

info

Powered up on a W call.

1 Confirm this is not a fault
On the Carrier 58STA 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 Carrier 58STA 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 on two-digit IFCs.
If fail: Fix the stat, harness, or data pair before you change parts.
3 Watch one full sequence
Leave power on. Watch Two-digit or vintage LED-status IFC (Comfort 80) through one cycle and write the first real fault that replaces this status word.
Expect: W: Inducer → metal-vent draft switch must close (31 if not) → HSI → single-stage valve → flame (34 if no prove) → heat-speed blower.

Limit lockout

lockout

Hardened 33. Limit/rollout stayed open.

1 Treat this as flame outside the exchanger
Do not reset the Carrier 58STA 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, dirty A-coil, rollout reset.
Expect: Dry collector, open flue, trap clear.
3 Reset only after the cause is fixed
Manual-reset rollout. Recurring rollout on Carrier 58STA 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.

Ignition lockout

lockout

Hardened 34.

1 Watch one full try — do not reset
Write the Carrier 58STA 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, rod, ground. Do not sit on resets.
Expect: W → No PVC → 58CTA cousin
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.

Gas-heat lockout / model plug

lockout

Valve relay fault, or missing/wrong model plug on boards that use one.

1 Read the plug / card on THIS cabinet
On Carrier 58STA the model plug or shared-data card must match this cabinet size. A 100 kBtu plug in an 80 cabinet overfires and limits. A leftover memory card after a control swap throws d0/d4-class codes. Most Comfort 80 STA boards are not TP6-style plug cabinets — check the door before you hunt a plug.
Expect: Plug / card part matches the rating plate and the replacement control bulletin.
2 Reseat, then confirm the menu
Kill power, reseat, restore power. On communicating plates open the setup and confirm unit size / motor HP. Valve harness and 24 VAC during trial.
Expect: IFC recognizes the plug. No size-mismatch code.
3 Do not run it mismatched
A wrong plug is not a ‘temporary’ fix. It will throw limit, ignition, or blower-band codes that look like bad parts. Fit the correct plug, then re-run the original complaint.
Expect: One clean sequence on the correct identity.

Flame with valve off

hazard

Flame sense while GV de-energized.

1 Shut the gas cock first
On Carrier 58STA 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.

PS did not open

lockout

Draft switch still made when it should be open.

1 Unplug the switch with the inducer off
On Carrier 58STA this code is the switch made when the inducer is not running. Unplug that switch only. Welded switch, residual chimney draft, inducer still spinning.
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 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.
Expect: Hose empty. Switch opens with no draft.
3 IFC input last
If the switch ohms open, the hose is dry, and the code does not change with the harness off, the Carrier 58STA IFC input is shorted. Do not keep swapping switches.
Expect: Known-good open switch + open harness = code gone. If not, IFC.

Secondary fuse open

warn

24 V fuse on the IFC.

1 Find the 24 V short before you replace the fuse
On Carrier 58STA 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 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 Carrier 58STA 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.

Metal-vent draft / inducer

lockout

Category I draft will not prove. NEVER a PVC condensate trap.

1 Prove inducer and the live code
Do not pull power — that clears the Carrier 58STA active code. Write 31. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Chimney liner, cap, masonry debris, wind.
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. Common-vented water heater — venting tables, not a 96% collector.
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. Inducer wheel packed or cracked, vent connector disconnected.
Expect: Switch closes on known draft. Vent unrestricted.
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.

Limit or rollout open

warn

Airflow or flame-containment. Dirty A-coil on an 80% is the winter/summer crossover call.

1 Treat this as flame outside the exchanger
Do not reset the Carrier 58STA 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, blower speed, A-coil on top of the furnace — 80% coils load up and limit. Rise vs plate. Rollout: exchanger / burners / flue. Manual reset.
Expect: Dry collector, open flue, trap clear.
3 Reset only after the cause is fixed
Manual-reset rollout. Recurring rollout on Carrier 58STA is a CO / fire call — cracked primary, misaligned burners, or a failed secondary. Confirm CO in the space before you leave. Held open → 13.
Expect: One clean cycle after the cause is fixed. No second reset as a repair.

Ignition prove fail

lockout

Trial without flame sense. Repeats → 14.

1 Measure µA while it is running
Do not clean first and guess. Series-µA the rod on Carrier 58STA 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, gas cock, manifold, rod, 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. Fix 31 metal-vent draft before a fair 34 test.
Expect: Manifold on the rating plate. Solid burner-box ground.
3 Prove it is not a switch opening
Watch the live Carrier 58STA 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

31 on Comfort 80

Inducer runs, no ignition, or intermittent no-heat on a metal-vent furnace.

1 Prove the call and the live code
This is not a 59SC5. There is no PVC trap. Do not look for a collector.
Expect: Write whatever Two-digit or vintage LED-status IFC (Comfort 80) is showing. Two-digit: last codes ~48 h or until power is pulled (11 = no history). LED vintage: flashes until power is pulled — write the count against THIS door card.
If fail: No call at the IFC → stat / harness. Do not change gas parts.
2 Isolate the first failed step in the sequence
Chimney liner, cap, and termination. Masonry chimneys without a liner are a 31 factory.
Expect: No PVC: Category I. There is no collector and no trap to dump. 31 lives in the chimney, cap, liner, common vent, and inducer wheel.
3 Confirm with a number, then the next part
Common-vented water heater: draft, spillage, and the venting table. The 31 may be the WH, not the switch. Inducer wheel — packed, broken, or wrong rotation after a motor swap. Then the draft switch and hose to the inducer housing. Water in that hose is flue condensate on a long metal run, not a 96% drain.
Expect: Vent: Cat I. Spillage at the draft hood / inducer inlet is a fail. No PVC trap exists. · Draft switch: Open with inducer off; closes on W. 31 = never closed. 23 = never reopened.
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.

33 dirty A-coil on 80%

Heat works then limits, or summer no-cool plus winter 33 on the same coil.

1 Prove the call and the live code
80% upflow with an A-coil on top: dirty coil is the usual 33. Pull the door and look before you change the limit.
Expect: Write whatever Two-digit or vintage LED-status IFC (Comfort 80) is showing. Two-digit: last codes ~48 h or until power is pulled (11 = no history). LED vintage: flashes until power is pulled — write the count against THIS door card.
If fail: No call at the IFC → stat / harness. Do not change gas parts.
2 Isolate the first failed step in the sequence
Filter and blower speed. Comfort 80 is tap/PSC or CT — not a 59TP6 model-plug CFM.
Expect: No PVC: Category I. There is no collector and no trap to dump. 31 lives in the chimney, cap, liner, common vent, and inducer wheel.
3 Confirm with a number, then the next part
Rise vs plate. Overfired STA (orifice / manifold / LP conversion) limits with a clean coil too. Rollout open? Stop. Exchanger / burners / flue — not another filter.
Expect: Vent: Cat I. Spillage at the draft hood / inducer inlet is a fail. No PVC trap exists. · Draft switch: Open with inducer off; closes on W. 31 = never closed. 23 = never reopened.
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

Vent

Cat I. Spillage at the draft hood / inducer inlet is a fail. No PVC trap exists.

Draft switch

Open with inducer off; closes on W. 31 = never closed. 23 = never reopened.

Heat speed

Tap / PSC / CT vs rise. Not Infinity CFM and not TP6 model plug.

Gotchas

58CTA is the two-stage 80% cousin — same metal-vent 31, extra W2. Do not diagnose high-fire PS on an STA.
58CVA is Infinity 80. Same chimney physics, different bus.
Vintage LED boards and two-digit boards do not share a card. Read the sticker in THIS blower.
58DL older Deluxe 80 — same Category I 31, older IFC generation.

Related plates

Install this plate

Install 58STA as Comfort 80 single-stage 24V. Metal vent. 31 is chimney draft.

Cat I metal vent · single-stage 80% · two-digit 31/33/34 · 24V W

Vent

B-vent / liner / common vent. Same 31 digit as 59SC5 — opposite physics.
Bryant 800S is the twin language. Product micro-page is retired; use the furnaces hub + dealer I/O.

First fire

1Confirm Cat I on the plate. W call. 31 closes. No PVC.

Do not on Carrier 58STA

Do not dump a trap. Do not land ABCD.

Maker literature

FieldBench does not host manufacturer files. Each link opens the maker’s own literature page in a new tab.

Carrier residential furnacesLiterature searchProduct pages carry current literature. I/O booklets are typically HVACpartners / dealer.Open manufacturer PDF
Carrier HVAC resourcesLiterature searchOwner-facing literature hub. Do not invent a 59-series I/O URL.Open manufacturer PDF
Carrier residential furnacesLiterature searchSearch Carrier 58STA on the maker’s literature page.Open manufacturer PDF

Warranty and bulletins

Affected models, serial range, symptom, remedy, date. Maker files open on the manufacturer site.

All bulletins

Residential limited warranty
warranty sheet
Carrier / Bryant registered heat-exchanger terms
Current 59-series / Evolution / Preferred registered warranty · Limited warranty certificate
Open facts Open manufacturer PDF
Dealer portals
dealer
Where remaining service letters live
Current-year service letters not on a public literature page · Maker dealer portal
Open facts Open manufacturer PDF