System Diagnosis
Limit Switch Open. The furnace has overheated or the rollout switch has tripped.
Lennox DS1 & DS2
Error Code On / Slow Flash
Troubleshooting guide for the Lennox DS1 & DS2 system fault On / Slow Flash.
ACLogics Fix Lennox code On / Slow Flash See how ACLogics handles it → Fix On / Slow Flash step-by-step
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.
Potential Causes & Solutions
- Dirty filter, blocked vents, bad blower motor, restricted airflow.
Verify Before Replacing Parts
- Confirm the exact Lennox model family and ds1 & ds2 context before acting on a generic code description.
- Confirm filter condition, blower operation, and coil cleanliness before replacing any controls.
- Measure airflow-related readings that match the symptom, such as temperature split or static pressure.
- After the correction, run the system long enough to confirm the code does not return under normal load.
Field Signals to Confirm
What usually confirms it
Weak airflow, abnormal temperature split, or repeated protective trips tied to blower performance.
What can fool you
Charge and control faults often look similar until airflow and coil condition are verified first.
When to Escalate the Call
- The code returns after airflow and cleanliness checks are corrected.
- You find evidence of duct or static issues that require a larger system review.
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.
