Error code reference

Lennox Heat Pump Error Code 4

Low or high pressure switch opens after compressor has run for less than two minutes, may indicate blockage or fan failure.

SourceLennox HP21 Series - Full Service Manual (Heat Pump)p. 14

Lennox codes Lennox heat pump codes

Diagnostic procedure

The full 4 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 for low system charge; check for blockage or fan failure.

SourceLennox HP21 Series - Full Service Manual (Heat Pump)p. 14

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

4 manuals in the MyPros+ library document this code for Lennox heat pump.

Models covered by the manuals that document this code

More models are covered than are listed here.

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The full 4 procedure

Where this code is documented

Models covered by the manuals that document this code

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