What It Means
Flame failure or watchguard mode due to repeated ignition or flame loss.
Lennox All Systems
Lennox Error Code Alt Slow Flash / Alt Slow Flash
Troubleshooting guide for the Lennox system fault Alt Slow Flash / Alt Slow Flash.
ACLogics Fix Lennox code Alt Slow Flash / Alt Slow Flash See how ACLogics handles it → Fix Alt Slow Flash / Alt Slow Flash step-by-step
Possible Causes
- Dirty flame sensor.
- Gas valve issue.
- Igniter failure.
- Gas supply issue.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Flame Failure / Watchguard Mode. The system has failed to ignite or lost flame signal multiple times.
All Recorded Causes
Dirty flame sensor, gas valve issue, igniter failure, gas supply issue.
Verify Before Replacing Parts
- Confirm the exact Lennox model family and ds1 & ds2 context before acting on a generic code description.
- Walk the entire heating sequence in order instead of jumping straight to the reported code, watching for dirty flame sensor, gas valve issue, igniter failure, gas supply issue.
- Verify each safety device and prove where the sequence stops under live operation, including whether the next candidate on the list.
- After the correction, run the system long enough to confirm the ds1 & ds2 fault does not return under normal load.
Not sure which system this Lennox code is on?
ACLogics has guided diagnostics for 16 Lennox fault codes and asks the right questions to narrow it down.
