FieldBench

Lennox

ML180

Furnace · Merit · 80% · metal vent · LED flash

Merit 80% Category I furnace. Same 1–9 flash numbers as ML196, opposite physics on 3-flash: chimney, inducer, common vent — not a drowned 96% trap. Metal vent, no secondary collector.

Not ML196 (96% PVC — same flashes, trap/collector checks). Not EL296V (E2xx 7-seg). Not SL280 / EL280 (Elite 80% two-stage; may have SureLight 7-seg on VS SKUs).

Walk this in Diagnose

This plate

AFUE
80% · Category I metal vent
Display
Single red LED flash chart — same numbers as ML196
Sister SKU
ML180UH upflow · ML180DF downflow

This board

Merit LED IFC

  • 1 unexpected flame, 2 PS closed, 3 PS open, 4 primary limit, 5 rollout, 6 PS lockout, 7 ignition lockout, 8 flame lost lockout, 9 polarity.
  • Same count as ML196. The vent is not the same. 3-flash here is metal vent / draft, not PVC.
  • LED off = no power. Steady on = idle on many of these.

Sequence

  1. W. Inducer → PS (3-flash if the metal-vent path will not make) → HSI → valve → flame → blower.

Faults on this IFC

  • 1 flash

    Unexpected flame

    hazard

    Flame with the valve off.

    • Shut the cock. Leaking valve.
  • 2 flash

    PS closed

    lockout

    Switch made with inducer off.

    • Welded switch or hose holding chimney draft. Not a 96% trap story.
  • 3 flash

    PS open

    lockout

    Draft not proven. On this 80% that is chimney / inducer / common vent — not a drowned 96% trap.

    • Metal vent, chimney liner, common-vent sizing, inducer wheel, intake at the burner box.
    • Do not cut a PVC trap. There isn’t one. If the last tech installed a condensate kit on an 80%, you are on the wrong physics.
  • 4 flash

    Primary limit

    warn

    Airflow / overtemp.

    • Blower speed, filter, coil, rise. 80% cabinets still starve on a media filter.
  • 5 flash

    Rollout

    hazard

    Flame containment. Hazard.

    • Exchanger, burners, blocked metal flue, downdraft. Reset only after the cause is gone.
  • 6 flash

    PS lockout

    lockout

    Hardened 3-flash.

    • Fix chimney / inducer / common vent, then reset.
  • 7 flash

    Ignition lockout

    lockout

    Failed to light.

    • HSI, gas, rod.
  • 8 flash

    Flame lost lockout

    lockout

    Had flame, then lost it.

    • Rod, ground, downdraft after blower-on.
  • 9 flash

    Polarity

    lockout

    L1/N reversed or ground missing.

    • Hot/neutral at the IFC. Chassis ground.

Workflows

3-flash on metal vent

Merit LED, 80% plate, no heat.

  1. Data plate: ML180 = Category I metal. Dumping a ‘96% trap’ story here wastes the call.
  2. Chimney, liner, common vent, inducer, burner-box intake. Spillage at the draft hood / collector is the clue.
  3. If you see E223 on a 7-seg, you are not on an ML — and if the plate says 80% you want SL280, not EL296V.

Test points

Vent
Metal Category I. Draft at the hood / collector, not a PVC trap.
Flash count
Same 1–9 as ML196. Physics follow the plate, not the number.

Gotchas

  • Techs who just left an ML196 will cut a trap story on 3-flash. There is no 96% collector on this furnace.
  • SL280 / EL280 is the Elite 80% two-stage. Some of those have SureLight 7-seg — still metal vent if E223 shows.

Related plates

  • lennox-ml196 — Merit 96% PVC. Same 1–9 flashes, opposite 3-flash physics.
  • lennox-sl280 — Elite 80% two-stage. Metal vent like this plate; may speak E2xx on VS SKUs.