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Error code reference
Trane Furnace Error Code 3 Flash
Pressure switch or inducer error-a pressure switch is either opened or closed contrary to normal operating sequence.
SourceTrane UHM/DHM Series Furnaces - Service Manual: Specificationsp. 40
Diagnostic procedure
The full 3 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
1
First diagnostic step
Verify all wiring and pressure switch tubing is correct per diagrams; cycle power to furnace, set comfort control to heat, and raise set-point 5 degrees above actual room temperature.
SourceTrane UHM/DHM Series Furnaces - Service Manual: Specificationsp. 40
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
3 manuals in the MyPros+ library document this code for Trane furnace.
Models covered by the manuals that document this code
75,000+ service documents · 20,000+ error codes · 100+ brands
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