FieldBench
Lennox codes

Lennox

4 flash

Protect

Primary limit

Airflow / overtemp.

Walk 4 flash in Diagnose

3 plates — walk the one on the cabinet

First check

1 Airflow before you touch the limit

On Lennox ML180 a limit is airflow or overfire until proven otherwise. Do not replace the limit first. Filter, blower wheel, A-coil, and the heat-speed setting for THIS motor (tap, model plug, or communicating CFM — not a sister SKU chart). Blower speed, filter, coil, rise. 80% cabinets still starve on a media filter.

Expect: Rise in the rating-plate window. Static vs this cabinet’s blower chart.

The rest of the walkthrough is Diagnose.

On the plates

  • Tap or PSC speed, filter, coil, rise.
  • Blower speed, filter, coil, rise. 80% cabinets still starve on a media filter.

Plates that use 4 flash

Same number, other makers

4 flash on Lennox is not the same code on these plates.