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Error code reference
Lennox Furnace Error Code DIAG#1: Alternate Flash / DIAG#2: Alternate Flash
Watchguard: burners failed to ignite.
SourceLennox GHR26 Series - Service Manual: Gas FurnacesPage 8 (Table 1), Page 11 (Table 6)
Diagnostic procedure
The full DIAG#1: Alternate Flash / DIAG#2: Alternate 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
Check gas supply, gas valve wiring, and ignition system.
SourceLennox GHR26 Series - Service Manual: Gas FurnacesPage 8 (Table 1), Page 11 (Table 6)
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
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