Error code reference

Lennox Furnace Error Code 3+1

Primary / Secondary limit switch open.

SourceLennox SL280UHV(X) Furnace - Service Manualp. 9

Diagnostic procedure

The full 3+1 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 continuity across switch(es); switches reset automatically upon cool down. Check for restrictions on blower inlet air (including filter) and outlet air.

SourceLennox SL280UHV(X) Furnace - Service Manualp. 9

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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

7 manuals in the MyPros+ library document this code for Lennox furnace.

Models covered by the manuals that document this code

More models are covered than are listed here.

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The full 3+1 procedure

Where this code is documented

Models covered by the manuals that document this code

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