Lennox
OA ERR
ProtectOA SENS ERR (JADE LCD example)
JADE LCD: OA / SENS ERR (or OA SYLK ERR). Outside-air thermistor failed or lost SYLK. Board thinks the roof is 20 °F or 120 °F.
Walk OA ERR in Diagnose
2 plates — walk the one on the cabinet
First check
1 Which sensor is this code?
On Lennox LGH OA ERR is a specific thermistor — indoor return/pipe, outdoor coil, discharge, or ambient. Unplug that sensor and ohm it vs the OEM temperature/resistance chart. Probe OA at the hood vs the module. Several degrees off is a sensor, not a damper.
Expect: Ohms move with temperature. Not open, not shorted.
The rest of the walkthrough is Diagnose.
On the plates
- Probe OA at the hood vs the module. Several degrees off is a sensor, not a damper.
- Ohm / SYLK the OA sensor. Cut 2-wire in the hood is weekly.
- Sun-soaked hood vs a shaded probe — measure the air the sensor sees.
Plates that use OA ERR
Same number, other makers
OA ERR on Lennox is not the same code on these plates.