FieldBench
Lennox codes

Lennox

Fan prove

Lockout

Indoor fan proving

Controller did not see blower current / pressure.

Walk Fan prove in Diagnose

2 plates — walk the one on the cabinet

First check

1 Write the live code and watch one cycle

On Lennox LGH read Prodigy unit controller (Landmark) before you pull power. Write Fan prove exactly. Watch one full sequence and note which step dies. Belt off, ECM alarm, or current switch around the wrong lead.

Expect: Call: Occupied / G starts the indoor fan. Y1 is cool. W is gas heat. They are different boards in the same box.

The rest of the walkthrough is Diagnose.

On the plates

  • Belt off, ECM alarm, or current switch around the wrong lead.
  • VFD in limp mode on some Trane/VFD cabinets will not make the prove switch.
  • Do not jumper fan-prove and walk away — heat will fire into a dead blower.

Plates that use Fan prove

Same number, other makers

Fan prove on Lennox is not the same code on these plates.