Carrier 58MVP Error Code 33: Limit Circuit Fault

What Does Code 33 Mean?

Status code 33 on the Carrier 58MVP is a limit circuit fault. It flashes when the high-limit switch or flame rollout switch is open, or when the furnace has dropped into high-heat-only mode after two successive low-heat limit trips. Unlike code 13, this is an active fault rather than a lockout — the furnace is signaling that it is running too hot right now.

When the limit opens, the burners shut off and the variable-speed blower runs for 4 minutes or until the switch re-closes, whichever is longer, to pull heat off the exchanger. If the switch stays open longer than 3 minutes, the code escalates to lockout code 13. If it is open less than 3 minutes, code 33 keeps flashing until the blower shuts off. Note that the flame rollout switch is a manual-reset device — if it tripped, a technician must find out why and reset it.

The most common cause is a dirty air filter starving the blower of return air; blocked registers do the same. Because the 58MVP modulates airflow to the heating stage, Carrier's guide notes that two low-heat limit trips force the furnace into high-heat-only mode — a distinctive behavior of this variable-capacity design. An uncommon, non-DIY cause is a loose blower wheel that cannot move rated airflow.

What You'll Notice

• The furnace runs, then the burners cut out while the blower keeps running for several minutes
• Warm air output is weak or the furnace short-cycles
• The control board LED flashes code 33
• The furnace seems stuck running only on high heat after repeated low-heat trips
• A visibly dirty filter, or registers closed or blocked around the house

Common Causes

How to Fix It: Restore Airflow to Clear the Limit Fault

What You'll Need

• Replacement air filter (correct size for your system) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Set the furnace circuit breaker to OFF and turn the gas shutoff valve perpendicular to the pipe (OFF). If you smell gas, leave immediately and call your gas company from outside.
2. Check and replace the air filter Remove the filter from the return duct or furnace slot. If it is dirty, clogged, or more than 3 months old, replace it with the correct size, with the airflow arrow pointing toward the furnace.
3. Open all supply and return vents Walk the house and make sure every supply register and return grille is fully open and not blocked by furniture, rugs, or curtains. Closed vents restrict airflow and drive overheating.
4. Look for obvious blockage at the blower inlet (visually only) With the power off, check the blower inlet area for heavy dust. Do not remove, tighten, or service the blower wheel or motor yourself — a loose or dirty wheel is a technician's repair.
5. Restore gas and power, then test Turn the gas valve and breaker back ON and set the thermostat to call for heat. If the flame rollout switch tripped, do not reset it yourself — have a technician inspect it first. Watch a full cycle to confirm the fault clears.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 33 or code 13 returns after a clean filter and open vents
• The flame rollout switch (red manual-reset button) has tripped
• The blower wheel is loose or the blower does not reach full speed
• The furnace stays locked in high-heat-only mode after airflow is corrected

✓ Verified against manufacturer service manual — March 2026