Bryant Evolution +95s Plus – Error 33, Hi Limit Trip (2024)

01-25-2016,10:02 PM #1


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Jan 2016
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I own a Bryant Model 355CAV060100 natural gas furnace that was installed in my house in 2010 and worked well for 2-3 years and then occasionally/rarely indicated a failure on the Evolution thermostat. The LED on the circuit board would indicate Error 33. The filter was changed regularly and the registers were all open and unobstructed. The system would reset automatically and run fine. Over then next couple winters the problem would occur more often especially when it would get bitter cold outside. I was primarily using a wood stove along with the gas furnace as an auxiliary unit, therefore the repair was not urgent to maintain comfort.

The inducer would spin, the igniter would glow, the solenoid would switch on the gas and the burner would ignite, once the heat exchanger warmed up the blower would start, after a few minutes the unit would trip off for a few minutes and then the cycle would repeat.

I attempted troubleshooting the unit including: replace air filter, verify registers open/unobstructed, verified combustion air intake/exhaust piping is free of obstruction, cleaned condensate trap and drain lines, verified blower spins freely with firmly attached blower squirrel cage blades and nothing seemed abnormal. I purchased a manometer and checked the three-stage gas valve pressure and monitored the voltage to the solenoids with a digital volt meter. The input gas pressure and each Low/Med/High gas pressure settings were within specification. The solenoid 24V control signals controlled the valves and the gas pressure followed as expected (ie. not a stuck solenoid issue).

I found the limit switch was opening due to high heat condition in the heat exchanger. The flame roll-out switch was not open, and the manual reset was in a normal position (not requiring manual reset). I replaced both of these sensors with OEM parts because they were inexpensive and possibly the source of the fault. The problem was not resolved. I tried one cycle with the filter removed and the filter door open to provide plenty of air intake, with no change to the problem.

I modified the original hi limit switch to accommodate a thermometer and allow me to jumper/bypass the limit circuit. I first measured the temperature at which the limit switch opened, then with the limit circuit bypassed I measured the temperature and it continued to rise. I shut the furnace off manually once it reached maximum operating temperature to avoid a fire safety issue. This confirmed for me that the unit is not just running a little hot or the limit switch is a little out of spec, the system is not balancing the heat generated with the airflow around the heat exchanger.

I measured temperature rise to be 62 deg F when the unit shuts down on medium heat, this value is in spec however I don’t know if it reached a steady state temperature before shut down.

I opened the evaporator and inspected the coil for restricted airflow. The coil looked fairly clean and a flashlight easily shined thru. I used CRC coil cleaner to clean the evaporator while I had it open for inspection. This did not fix the issue. I measured the static pressure with a pressure probe and found it less than the maximum 0.5 inches H2O (med=0.1 and high fan speed=0.2 inches H2O).

I determined the unit uses an electronic control module to run the DC motor and not start/run capacitors that could affect the RPM of the blower motor. So a simple capacitor replacement is not an option for my unit.

I concluded that the issue is with either the thermostat, main circuit board, motor control module or the blower motor. These parts are too expensive to randomly replace. I then called the company who installed the system, they checked many of the same items that I verified/replaced. On the third service call the circuit board was swapped and the furnace now runs properly. I don’t know the exact circuit board failure mode, but assume the blower speed directed by the board was an incorrect slower speed than required.

I don’t have a question, I just wanted to share this overall experience as it may help others with similar issues.

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Bryant Evolution +95s Plus – Error 33, Hi Limit Trip (2024)


Bryant Evolution +95s Plus – Error 33, Hi Limit Trip? ›

error 33 is a high limit fault. It CAN include the roll-out switches, but usually it is the high limit switch located inside the heat exchanger blower compartment. This tripping is mainly caused by either a clogged indoor air filter, or a failing indoor blower or blower component.

What is error code 33 on Bryant Plus 95s evolution? ›

The roll out limits are located on the burner box. If you reset all these by pressing in on the little buttons to make sure they are not popped up and you still get the 33 limit code then you need to bypass the main limit to see if it is the one that is open.

What is error 33 limit circuit fault? ›

Code 33 is a Limit Circuit Fault code. This means that the flame rollout switch is open. If the high limit or flame rollout switch is open, you will experience error code 13.

Why does my furnace high limit keep tripping? ›

Dirty Air Filters: One of the simplest reasons is a dirty air filter. Over time, filters can accumulate dust and debris, causing a restriction in airflow. When air can't circulate properly, heat builds up inside the furnace, causing the high limit switch to trip as a protective measure.

How do you reset the limit switch on a furnace? ›

Begin by turning off the power to the furnace. Locate the limit switch, which is usually near the heat exchanger. Carefully remove the cover and gently press the reset button. If this doesn't solve the issue, you may need to replace the limit switch altogether.

How do I fix code 33? ›

Error 33 is likely the furnace is overheating. Please set your fan switch to on and see if the house fan comes on. If the house fan does not come on then you should look at the relay for the house fan. This can be found by tracing the fan circuit.

What is system error 33? ›

Code 33 “Windows cannot determinewhich resources are required for this device. (Code 33)”

What causes a high limit switch to go bad? ›

Dirty or Faulty Flame Sensor

One of the most frequent culprits behind high limit switch trips is issues with the flame sensor. This critical component monitors the burners to confirm they've properly ignited before allowing the gas valve to remain open and fuel to flow.

How to clean a high limit switch? ›

Remove the furnace access panel to locate the high limit switch on the outside of the plenum. Unscrew the switch from the plenum. Use steel wool or sandpaper to gently clean away soot and other materials stuck on the rod. Replace the switch and access panel.

How do you know if a limit switch is bad? ›

Check for inconsistent operation, failure to activate/deactivate, or physical damage. Test continuity with a multimeter; a lack of continuity indicates a bad limit switch.

What triggers a limit switch in a furnace? ›

The limit switch monitors the temperature and shuts down the burners if the furnace starts to overheat. A blower fan activates to cool the system down to a safe temperature. After the furnace is at a safe temperature again, the limit switch triggers the burners to repeat the process.

Does a high limit switch reset itself? ›

This limit should reset on its own when the temperature returns to normal. Occasionally, the limit will not reset on its own.

What is error 33 on air conditioner? ›

error 33 is a high limit fault. It CAN include the roll-out switches, but usually it is the high limit switch located inside the heat exchanger blower compartment. This tripping is mainly caused by either a clogged indoor air filter, or a failing indoor blower or blower component.

What is the error code 3 3 on a Bryant furnace? ›


Indicates a limit or flame rollout, is open or the furnace is operating in high-heat only mode due to 2 successive low heat limit trips. Blower will run for 4 minutes or until open switch remakes whichever is longer.

What is the E3 code on a Bryant thermostat? ›

The E3 is telling us the outdoor temperature sensor is not being read. First make sure it is connected and if so, replace the sensor.

What is error code 33 on inverter? ›

Event number 33 and the corresponding 4-digit event numbers indicate that the power supply at the DC input is not sufficient for stable operation of the inverter and the inverter therefore cannot connect to the utility grid yet.


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