Lennox
E252
ProtectDischarge air too high
Leaving-air temperature above the gas-heat limit (DAT sensor).
Walk E252 in Diagnose
2 plates — walk the one on the cabinet
First check
1 Airflow before you touch the limit
On Lennox EL195NE 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). Rise vs plate. Heat CFM in the IFC, not a guess.
Expect: Rise in the rating-plate window. Static vs this cabinet’s blower chart.
The rest of the walkthrough is Diagnose.
On the plates
- Rise vs plate. Heat CFM in the IFC, not a guess.
- Input rate / manifold. Sensor itself only after airflow and fire are right.