How to Fix Carrier Error Code 33 or 13 After Upgrading to a Higher MERV Rated Filter

Upgraded to a Higher MERV-Rated Filter and Now Your Carrier Furnace is Throwing 33 or 13 Error Codes?

Due to COVID-19, many people are taking precautions to better their in-home air quality. The big problem however, is a higher MERV rated filter can restrict the air flow going over the furnace's heat exchanger and cause the furnace to go off on high limit.

On Carrier, Bryant and Payne furnaces, the lack of airflow will cause an error 33, and sometimes lead to error 13 due to safety lockout. Error 33 is a Limit Circuit Fault. It means that the high limit or flame rollout switch is open. This can lead to error code 13, Limit Circuit Lockout. Error 13 means that the limit or flame rollout has been open for more than 3 minutes.

To address this issue, we need to ensure the furnace has proper air flow, and increase it if necessary. Below are some troubleshooting tips you can run through before you spend your money on parts.

Check for proper switch operation

  1. Check for continuity in the high limit switch after furnace has cooled down (15 minutes). If the high limit switch is still open, then the switch is bad.
  2. If flame rollout switch is tripped, look for back drafts, blocked flue and check heat exchanger to determine the cause of flame rollout.
  3. Reset the flame rollout switch(es) by pressing the button behind the disc. If switch is still open after pressing the button, then the flame rollout switch is bad.

Check for air flow issues

  1. Check condition of filter. Make sure it is not dirty and blocking air flow.
  2. Open all vents and return registers.
  3. Make sure the ducts and register grilles are clean.
  4. Clean the A/C evaporator coil.
  5. Check condition of the blower wheel. Make sure it is clean, tight and not missing any blades.
  6. Check blower motor and capacitor to make sure the blower motor is running up to speed.
  7. Make sure there is proper combustion air. on 90%+ furnaces, check the incoming PVC pipe. On 80% furnaces, make sure the furnace isn't locked up in a closet and not receiving any combustion air. 80% furnaces pull combustion air from the ambient air around it.
  8. If all those check out, increase the speed of the blower motor during heat mode by switching to a higher speed on the control board.

Still Need Help?

If you find any issues and need replacement parts, browse our selection of furnace repair parts. Additionally, if you have any questions for diagnosing your issue, feel free to contact us.
Worldwide Shipping
Genuine OEM Parts
Secure Shopping
1-Year Returns