Error code reference

Lennox Heat Pump Error Code Simultaneous FAST Flash

Ambient sensor problem: sensor detected open, shorted, or out of temperature range; control reverts to time/temperature defrost operation (system will still heat or cool).

SourceLennox XP14 Series Heat Pump - Full Service Manualp. 9

Lennox codes Lennox heat pump codes

Diagnostic procedure

The full Simultaneous FAST Flash procedure

Step 1 is visible so you can confirm you are on the right page. The remaining steps, the ones that tell you whether to actually replace a part, unlock with any pass.

MyPros+ · DiagnosticsStep 1 preview

First diagnostic step

Check ambient sensor resistance at pins 3 & 4 (Black wires); replace sensor harness if open or shorted.

SourceLennox XP14 Series Heat Pump - Full Service Manualp. 9

Unlock with pass

More steps, wiring diagram references, and verified part numbers

Includes expected resistance and voltage values, connector pinouts, and supersession notes for replacement parts.

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Where this code is documented

1 manual in the MyPros+ library documents this code for Lennox heat pump.

Models covered by the manuals that document this code

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The full Simultaneous FAST Flash procedure

Where this code is documented

Models covered by the manuals that document this code

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