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Error code reference
Lennox Furnace Error Code E120
Unresponsive device (communication only), usually caused by delay in outdoor unit responding to indoor unit polling.
SourceLennox EL296DFV(X) - Service Manual: icomfort-Enabled Gas Furnacep. 10
Diagnostic procedure
The full E120 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
Recycle power. Check all wiring connections.
SourceLennox EL296DFV(X) - Service Manual: icomfort-Enabled Gas Furnacep. 10
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 furnace.
Models covered by the manuals that document this code
75,000+ service documents · 20,000+ error codes · 100+ brands
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