Carrier Furnace Error Code 33 at Reset

furnace open with wiring revealed

The Carrier furnace is one of the most common heating devices in most homes. When the furnace has a problem, you can easily detect it and fix it by looking at the error codes shown.

Among the most common error codes for the Carrier furnace are 33 and 13. Code 13, normally occurs as a result of code 33. In most cases, you will first spot code 33 which will stay for a while before turning to code 13.

Code 33 on Carrier and Bryant furnaces is caused by a lack of airflow. If the issue is not resolved in time, it may develop to code 13, caused by safety lockout. 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. Code 13 simply stands for Lock Circuit Lockout, which means the limit or flame rollout has been open for more than 3 minutes.

Given that the two error codes are related, you may have a hard time trying to resolve them. In most cases, people get confused when one error code leads to another. For you to solve error code 13, you must first solve error code 33.

woman adjusting furnace controls

Causes of Error Codes 33 and 13.

During the COVID-19 pandemic, many people sought to improve the quality of the air they breathed. In the process, many people opted for higher MERV-rated filters. While better filters may improve the air quality in your home, using them on an unsuitable furnace may be the start of the problem.

While higher-rated filters will pass air, the Carrier furnace may interpret some aspects of the new filter as an error. If you recently changed air filters and you happen to see error code 33, you should try and replace the new filters with the recommended ones for your furnace.

Diagnosis of Error Code 33

Once you spot the error code 33, you want to carry out a diagnosis to find out what the real problem is. In most cases, the problems causing codes 33 and 13 will be related. Start by diagnosing error code 33 since it is likely to be the cause of the whole problem.

Check for Proper Switch Operation

One of the ways to diagnose the problem is by checking switch operations. The Carrier furnace has several switches that play different roles. To start your diagnosis, switch off the unit and let the furnace cool down for 15 minutes.

After it cools down, check for continuity in the high limit switch. If the switch is still open after the furnace has cooled, the switch is bad, and replacing it will solve all the issues.

The other switch you want to look at is the flame rollout switch. After the system cools and you find the flame rollout tripped, there are some issues with your furnace. In this case, the most likely issues could be backdrafts and blocked flow. You may also want to examine the heat exchanger to determine the cause of the flame rollout.

If you realize that the flame rollout switch is open, reset it by pressing the button behind the disc. If the switch still remains open after pressing the switch, it has gone bad and has to be replaced.

hands moving furnace filter

Check for Airflow Issues

Apart from the switch issues, the other potential cause of errors 33 and 13 is the airflow problem. If you recently replaced your filters, you will have to remove the new filters and replace them with compatible ones.

If you did not replace filters recently, check your filters to see whether there is dirt blocking airflow. Clean any dirt that may be blocking airflow and allows your furnace to run again to see if the problems persist.

If the air filter is okay, try opening all the vents and return registers. The vents may get clogged and affect airflow, which could result in error code 33. Make sure all the ducts and register grills are clean. You may also want to clean the AC evaporator coil.

If all the airflow vents are clean, but you are still experiencing the problem, you may want to consider looking at the blower wheel and the blower motor. This is just to ensure that the blower is running. If the blower fails, you may still encounter the same problems.

gray home furnace

Bottom Line

If you are experiencing error code 33, chances are that you are having airflow problems or switch problems. By following the above steps, you will be able to diagnose and deal with all switch and airflow issues and hence resolve the problems using the error codes.