Ruud U96VA0702317MSA Error Code 33: Over-Temperature Switch (Roll-Out) Open
What Does Code 33 Mean?
A code 33 on the Ruud U96VA0702317MSA means the Manually Reset Limit Control (MRLC), also known as the rollout limit switch, has tripped. This switch detects flame rollout — flames escaping from the heat exchanger area into the burner compartment. Flame rollout is a serious safety event that can damage the furnace and create fire or carbon monoxide hazards. Gas heating is blocked until the root cause is corrected, though cooling and fan-only modes may still work.
The rollout limit switch trips when combustion gases cannot exit through their normal path in the heat exchanger and flue. Blocked exhaust venting is the most common cause — a restricted or closed vent pipe forces hot gases backward, driving flames out of the combustion area. Unstable flame patterns from damaged burners or seal failures, or a compromised heat exchanger with cracked tubes that allow cross-flow, can also produce rollout conditions. In rare cases, loose or faulty wiring can cause the code to appear without actual flame rollout occurring.
This switch is a manual-reset type by design — it cannot reset itself automatically. This forces a technician to physically acknowledge the safety event before the furnace is allowed to attempt heating again. Pressing the reset button without diagnosing and correcting the root cause is dangerous because the rollout will simply recur.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Insufficient venting or blocked exhaust | Most common | ✗ Call a pro → |
| Unstable flame pattern or damaged heat exchanger | Common | ✗ Call a pro → |
When to Call a Professional
Contact a licensed HVAC technician if:
- Call a technician immediately — flame rollout is a serious safety condition and the furnace must not be restarted until the cause is found and repaired
- The technician must inspect the venting system for blockages or restrictions, examine the heat exchanger and burner assembly for damage, and manually reset the rollout switch only after confirming the root cause has been corrected
✓ Verified against manufacturer service manual — March 2026