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Error code reference
Lennox Furnace Error Code E203
Appliance capacity/size is NOT programmed; invalid unit codes.
SourceLennox SLP98DFV - Service Manual: High-Efficiency Gas Furnacep. 18
Diagnostic procedure
The full E203 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
Check for proper configuring under Unit Size Codes for Furnace on configuration guide or in installation instructions. Remove thermostat from system while applying power and reprogramming.
SourceLennox EL296DFV(X) - Service Manual: icomfort-Enabled Gas Furnacep. 11
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
2 manuals in the MyPros+ library document this code for Lennox furnace.
Models covered by the manuals that document this code
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