FieldBench
How To
Electrical8 min · 5 steps

Read furnace and rooftop flash codes

A flash count is not a two-digit and not a 7-seg E. Goodman 3-flash is not Lennox 3-flash is not a Carrier IGC 3-flash. Count the group, then open THIS door card.

Still failing after this procedure?

How To stays open. Diagnose walks the next measurement.

Before you start

  • A rollout / 5-flash / 6-flash (Goodman) is a flame-containment call. Do not reset and leave.
  • Do not jumper a pressure switch, limit, or rollout to ‘see if it runs.’

On the truck

  • The live LED — do not kill power
  • Phone to photograph the door card / IGC sticker
  • The model plate so you know which family you are in

Steps

  1. 1 Decide what you are looking at

    One red LED that counts, pauses, repeats = a flash code. Two groups (three blinks, pause, one blink) = a two-digit (Carrier 31). A 7-seg showing E2 or 04 = not a flash chart. A rooftop IGC LED in the heat section is not the unit-board LED in the control box.

    Expect: One family named: 1–9 LED, two-digit, 7-seg, or rooftop IGC.

    If it fails: If the display is a communicating thermostat error, leave this how-to and load the indoor plate.

  2. 2 Count one full group

    Watch until the long pause, then count the next burst. Heartbeat (slow even blink while running) is not a fault. Rapid continuous flash on many Goodman/Amana boards is polarity, not ‘a high number.’ Write 3-flash, not ‘it blinked a lot.’

    Expect: A single integer (1–9) or a two-digit (31, 33, 34) written down.

    If it fails: Power already cycled? The live code is gone. Use recall if this IFC stores a stack — then still confirm the door card.

  3. 3 Match the family — not a universal chart

    Goodman/Amana 1–9 (GMSS96 / AR9S96 class): 1 retry lockout, 2 PS closed with inducer off, 3 PS open, 4 limit, 5 flame with valve off, 6 rollout, 7 low flame, 8 igniter, 9 polarity. Lennox Merit 1–9 uses the same numbers with different jobs (1 = unexpected flame, 5 = rollout, 6 = PS lockout, 7 = ignition lockout). Carrier Comfort 80/90 is two-digit (31 inducer, 33 limit, 34 ignition) — never count it as 3-flash.

    Expect: The number mapped on THIS door card, not a screenshot from last week’s brand.

    If it fails: Load the model in FieldBench (GR9S96, ML196, 59SC5, 48FC IGC). Sister SKUs do not share flash tables.

  4. 4 3-flash is draft — the vent decides the repair

    On a 96% PVC furnace, 3-flash / E2 is trap, collector, slope, inducer. On an 80% metal-vent furnace, the same 3-flash is chimney, liner, cap, common vent. Lennox ML196 and ML180 prove this every day. Do not cut a trap story on a B-vent, or a chimney story on a drowned 96% collector.

    Expect: Vent material named before any part is changed.

    If it fails: If the LED is on a rooftop IGC, 2-flash is usually the draft switch in the heat section — still not a split-system 3-flash.

  5. 5 Rooftop IGC is a different sticker

    Packaged CES IGC (typical 48FC / 581J heat section): 2-flash ≈ PS/draft, 3-flash ≈ limit, 4-flash ≈ rollout/aux (or consecutive limit — read THIS sticker), 6-flash ≈ ignition lockout, 8-flash ≈ internal/valve. Power-cycle once on 8-flash; if it returns, valve ohms then IGC. Do not apply a GMSS96 8-flash (igniter) to this LED.

    Expect: IGC sticker photographed. Cool/economizer codes are on the unit board, not this LED.

    If it fails: JADE in the hood speaks MA SENS ERR, not flashes. Reliatel speaks Heat Fail / Fan Fail. Type those strings instead.

Field notes

  • Heartbeat ≠ fault. Count the group after the long pause.
  • Same integer, different board: Goodman 6-flash is rollout; Lennox Merit 6-flash is PS lockout; Carrier IGC 6-flash is ignition lockout. The door card is law.
  • Two-digit 31 is inducer/PS on many Carrier Comfort boards. It is not ‘3 then 1 flash’ from a Goodman chart.
  • Type the live count in Diagnose with the model (GR9S96 3-flash, 48FC 8-flash, ML180 3-flash).

Related

Sources

Practice distilled from public HVACR School and AC Service Tech material. OEM I/O and EPA 608 still win.