Bryant 355MAV Error Code 33: Limit Circuit Fault
What Does Code 33 Mean?
Status code 33 on the Bryant 355MAV indicates a limit circuit fault. A high-limit switch or flame rollout switch is currently open because the furnace has detected overheating. The blower runs for 4 minutes, or until the switch closes again, whichever is longer, to bring temperatures back down.
This is the active warning stage. If the switch stays open longer than 3 minutes, the board escalates to lockout code 13 and shuts the furnace down. If the switch recloses within 3 minutes, code 33 keeps flashing until the blower finishes its run. Because the 355MAV is a two-stage furnace, the board may also drop into high-heat-only mode after 2 successive low-heat limit trips, which is another way this code shows up.
The most common cause is a dirty air filter restricting airflow across the heat exchanger. A loose blower wheel or an improperly positioned limit switch and limit shield are less common causes. Importantly, if it is the flame rollout switch that tripped rather than the high-limit, that switch latches and must be manually reset by pressing its button — and a rollout trip points to a combustion or heat-exchanger problem that needs a technician.
What You'll Notice
- The burners shut off but the blower keeps running for several minutes to cool the furnace
- Heating cycles are short and the home struggles to reach the setpoint
- The status LED flashes code 33 (three short flashes, three long flashes) while the blower runs
- The furnace may run only on high heat, skipping its quieter low-heat stage
- If the flame rollout switch tripped, the furnace stays down until its reset button is pressed
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty air filter causing overheating | Most common | ✓ DIY fix → |
| Loose blower wheel | Uncommon | ✗ Call a pro → |
| Improper or misaligned limit and/or limit shield | Uncommon | ✗ Call a pro → |
How This Is Diagnosed
The check starts at airflow: the filter is inspected first, then all supply and return vents are confirmed open, since restricted airflow is the usual reason the limit opens. If airflow is fine, the blower wheel is examined for dust buildup or looseness that would reduce output.
The board also distinguishes which switch opened. A high-limit trip generally traces back to airflow, while a flame rollout trip is treated more seriously because it indicates flames or hot gases spilling out of the burner area — a combustion or heat-exchanger concern. The limit switch and its shield are checked for correct alignment last.
How to Fix It: Replace the Air Filter and Restore Airflow
What You'll Need
- Replacement air filter (correct size for your system) 🛒 Find at FiltersFast · 🛒 Find at Amazon
- Flashlight
Steps
- Turn off electrical power at the breaker and shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF. Turn the gas shutoff valve to the OFF position (perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
- Check and replace the air filter Remove the air filter from the return air duct or furnace filter slot. If it is visibly dirty or clogged, replace it with a new filter of the correct size. Make sure the airflow direction arrow on the new filter points toward the furnace.
- Verify all supply and return vents are open Walk through every room and ensure all supply registers and return grilles are fully open and not blocked by furniture, curtains, or rugs. Even a few closed vents can significantly restrict airflow and cause overheating.
- Inspect the blower area With the power off, look at the blower wheel through the access panel opening. Check for excessive dust buildup on the blower blades, which can reduce airflow. Also verify the blower wheel is securely attached to the motor shaft and not wobbling.
- Restore power and gas, then test Turn the gas supply valve to ON and flip the circuit breaker to ON. Set your thermostat to call for heat and monitor the furnace through its heating cycle.
When to Call a Professional
Contact a licensed HVAC technician if:
- Code 33 returns after replacing the filter and opening all vents
- The flame rollout switch tripped, which points to a combustion or heat-exchanger problem
- The blower wheel is loose, damaged, or excessively dirty
- You hear unusual noises from the variable-speed blower motor
- The fault escalates to lockout code 13 repeatedly
Frequently Asked Questions
Should I just keep resetting code 33 on my Bryant 355MAV?
No. Code 33 signals real overheating. Address the cause — most often a dirty filter or blocked vents — rather than repeatedly resetting, or the furnace will keep tripping and eventually lock out on code 13.
Why is my furnace only running on high heat now?
After 2 successive low-heat limit trips, the 355MAV can switch to high-heat-only mode as a protective response, which is reported under code 33. Restoring proper airflow usually lets it resume normal two-stage operation.
What is the flame rollout switch and why does it need a manual reset?
It is a safety switch that trips if flames or hot gases spill out of the burner area. Unlike the high-limit, it latches and must be reset by pressing its button — and because a rollout trip can indicate a serious combustion or heat-exchanger issue, it should be inspected by a technician before running the furnace.
Sources
✓ Verified against manufacturer service manual — March 2026