Bryant 315AAV Error Code 33: Limit Circuit Fault

What Does Code 33 Mean?

A limit circuit fault (status code 33) on the Bryant 315AAV means a switch in the limit string — the main limit, draft safeguard, flame rollout, or blocked vent switch (if used) — has opened, or the furnace is running in high-heat-only mode after two successive low-heat limit trips. Unlike the code 13 lockout, code 33 is the recoverable warning stage; the control runs the blower for 4 minutes or until the open switch recloses, whichever is longer, to shed heat.

The critical relationship is the escalation: if the switch stays open longer than 3 minutes, code 33 changes to status code 13, a full limit circuit lockout that auto-resets only after three hours. Catching and clearing the airflow problem at the code 33 stage often prevents the harder lockout. On this variable-speed furnace the ECM blower is the tool the control uses to cool the heat exchanger while the limit is open.

Bryant lists the causes as a dirty filter or restricted duct system (the most common and homeowner-addressable one), a restricted or improperly sized vent, excessive wind, inadequate combustion air, and a defective switch or connections. Only the filter and vent restrictions are safe for a homeowner to address; the venting, combustion air, and switch causes are technician work.

What You'll Notice

• The furnace blower runs for several minutes at a time while the burners are off
• Heat output is intermittent — the furnace warms, then backs off as the limit opens
• The status LED flashes three short then three long flashes
• You may find a dirty filter or blocked registers, and the code may turn into code 13 if it persists

Common Causes

How This Is Diagnosed

The cause is isolated from the airflow path inward: check the filter first, then the supply and return registers, then the duct system and blower for restriction. Only after airflow is confirmed good does a technician evaluate the vent sizing, combustion-air supply, wind effects, and the limit, rollout, and draft-safeguard switches and their connections themselves.

How to Fix It: Clear the Airflow Restriction: Filter and Vents

What You'll Need

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

Steps

1. Turn off electrical power at the breaker or furnace switch and shut off the gas supply Set the furnace disconnect switch (or its breaker) to OFF and turn the manual gas shutoff valve to OFF (handle perpendicular to the pipe). If you smell gas at any point, leave the house immediately and call your gas company.
2. Replace a dirty air filter Remove the filter from the return duct or filter slot. If it is dirty or more than about three months old, replace it with the correct size, with the airflow arrow pointing toward the furnace. A clogged filter is the most common trigger for a limit fault.
3. Open all supply and return vents Confirm every supply register and return grille is fully open and not blocked by furniture, rugs, or curtains. Too many closed rooms starves the blower and overheats the heat exchanger.
4. Check for obvious duct or blower restriction Look for a collapsed flex duct, a closed damper, or heavy dust on the visible blower wheel. Do not disassemble the blower or ductwork — if you find a deeper restriction, that is a technician's job.
5. Restore power and gas, then watch a full cycle Turn the gas valve back ON, restore power, set the thermostat to call for heat, and watch a complete cycle to confirm the furnace holds a steady flame without the limit reopening.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 33 returns, or escalates to code 13, after you replace the filter and open the vents
• The vent appears restricted or improperly sized, or high wind seems to trigger it
• A flame rollout or draft-safeguard switch has tripped or is suspected defective
• The furnace keeps limiting despite clean filter and clear, open ductwork

✓ Verified against manufacturer service manual — March 2026