Ruud U96VA0702317MSA Error Code 33: Over-Temperature Switch (Roll-Out) Open
What Does Code 33 Mean?
Code 33 on the Ruud U96VA0702317MSA means a manually reset rollout limit (M.R.L.C.) has opened because flames rolled out of their normal path in the heat exchanger and into the burner compartment. The manual notes this should rarely if ever be seen and indicates a very serious problem that must be repaired before the furnace can run again. The limit is manual-reset by design, so a technician must acknowledge the fault after fixing the cause — it does not clear on its own.
While the fault is active the furnace will not provide gas heat; cooling and fan may still work. Flame rollout is a fire and carbon-monoxide hazard, which is exactly what the rollout limit exists to guard against.
The most common cause is insufficient venting — a blocked or restricted intake or exhaust that keeps combustion gases from leaving normally and forces flames backward. Damaged heat-exchanger tubes, a breached collector box, improper burner or door seals, or an unstable flame pattern can also cause it. None of these are DIY, and the rollout switch should not be reset until the cause is found and repaired.
What You'll Notice
- The furnace will not produce heat and the display shows code 33
- The fault does not clear by itself because the rollout limit is manual-reset
- You may notice signs of a blocked or restricted vent, or scorching near the burner area
- Cooling and fan modes may still operate
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 → |
How This Is Diagnosed
A technician treats code 33 as a serious combustion-safety issue. They check that the pressure switches have not been welded closed or bypassed, verify the inducer runs at proper speed, and inspect the intake and exhaust venting for blockage and for exceeding the maximum allowed lengths.
They also inspect the seals between the inducer, center panel, and heat exchanger, confirm the burner assembly and combustion-door seals are intact, and check the heat exchanger for damage such as crushed tubes or a breached collector box before repairing the cause and manually resetting the limit.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- Code 33 is displayed — flame rollout is a safety hazard that requires immediate professional service
- The vent intake or exhaust looks blocked, restricted, or improperly terminated
- There are signs of scorching, soot, or heat damage near the burner compartment
- Do not manually reset the rollout switch until a technician has found and corrected the cause
Frequently Asked Questions
Why can't I just reset the rollout switch and keep using the furnace?
The rollout limit is manual-reset specifically so the dangerous cause — usually blocked venting or a damaged heat exchanger — gets found and fixed first; resetting without repair risks fire and carbon-monoxide exposure.
What most often causes code 33?
Insufficient or blocked venting is the most common cause, which forces combustion gases and flame back into the burner area; damaged heat-exchanger tubes or bad seals can also cause it.
Is it safe to be in the house with code 33?
The furnace shuts off gas heat as a protection, but because flame rollout involves fire and carbon-monoxide risk, you should have it inspected promptly and ensure any CO alarms are working.
✓ Verified against manufacturer service manual — March 2026