FieldBench

Carrier

58STA

Furnace · 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.

Walk this in Diagnose

This plate

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.

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

  • 11

    No stored history

    info

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

    • Not a fault. Recreate the W call.
  • 12

    Blower on after power-up

    info

    Powered up on a W call.

    • Normal after a brownout on two-digit IFCs.
  • 13

    Limit lockout

    lockout

    Hardened 33. Limit/rollout stayed open.

    • Filter, heat speed, dirty A-coil, rollout reset.
  • 14

    Ignition lockout

    lockout

    Hardened 34.

    • HSI, gas, rod, ground. Do not sit on resets.
  • 21

    Gas-heat lockout / model plug

    lockout

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

    • Most Comfort 80 STA boards are not TP6-style plug cabinets — check the door before you hunt a plug.
    • Valve harness and 24 VAC during trial.
  • 22

    Flame with valve off

    hazard

    Flame sense while GV de-energized.

    • Leaking valve. Shut the cock.
  • 23

    PS did not open

    lockout

    Draft switch still made when it should be open.

    • Welded switch, residual chimney draft, inducer still spinning.
  • 24

    Secondary fuse open

    warn

    24 V fuse on the IFC.

    • Tstat short, HUM/EAC, valve harness. Replace fuse only after the short is gone.
  • 31

    Metal-vent draft / inducer

    lockout

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

    • Chimney liner, cap, masonry debris, wind.
    • Common-vented water heater — venting tables, not a 96% collector.
    • Inducer wheel packed or cracked, vent connector disconnected.
    • PS hose to the inducer housing only. There is no secondary drain to pull.
  • 33

    Limit or rollout open

    warn

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

    • 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.
    • Held open → 13.
  • 34

    Ignition prove fail

    lockout

    Trial without flame sense. Repeats → 14.

    • HSI, gas cock, manifold, rod, ground.
    • Fix 31 metal-vent draft before a fair 34 test.

Workflows

31 on Comfort 80

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

  1. This is not a 59SC5. There is no PVC trap. Do not look for a collector.
  2. Chimney liner, cap, and termination. Masonry chimneys without a liner are a 31 factory.
  3. Common-vented water heater: draft, spillage, and the venting table. The 31 may be the WH, not the switch.
  4. Inducer wheel — packed, broken, or wrong rotation after a motor swap.
  5. 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.

33 dirty A-coil on 80%

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

  1. 80% upflow with an A-coil on top: dirty coil is the usual 33. Pull the door and look before you change the limit.
  2. Filter and blower speed. Comfort 80 is tap/PSC or CT — not a 59TP6 model-plug CFM.
  3. Rise vs plate. Overfired STA (orifice / manifold / LP conversion) limits with a clean coil too.
  4. Rollout open? Stop. Exchanger / burners / flue — not another filter.

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

  • carrier-58cva — Infinity 80 two-stage — same metal-vent 31, ABCD bus this Comfort board does not have.
  • carrier-59sc5 — Comfort 96 single-stage — same 31 number, PVC trap / collector instead of a chimney.