Lennox

3 flash

Lockout

PS open

Draft not proven. On this 96% that is trap / PVC / collector — not a chimney.

3 plates — walk the one on the cabinet

First check

1 Prove inducer and the live code

Do not pull power — that clears the Lennox ML180 active code. Write 3 flash. Is the inducer spinning on this call? Silent inducer is not a pressure switch. Metal vent, chimney liner, common-vent sizing, inducer wheel, intake at the burner box.

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).

The rest of the walkthrough is Diagnose.

On the plates

Condensate trap, collector, PVC intake/exhaust, inducer.
Do not pull the ML180 metal-vent playbook. Same flash, opposite wet/dry checks.
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.

Plates that use 3 flash

Same number, other makers

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