Bryant 315AAV Error Code 13: Limit Circuit Lockout

What Does Code 13 Mean?

On the Bryant 315AAV, a limit circuit lockout (code 13) sets when a safety switch in the limit string — the main limit, draft safeguard, flame rollout, or blocked vent switch (if used) — stays open longer than 3 minutes, or after 10 successive limit trips in a single heating cycle. The furnace shuts the burners down completely to protect the heat exchanger.

This lockout is the escalation of status code 33, the limit circuit fault. Code 33 is the recoverable warning that a limit switch has opened; if that open condition persists past 3 minutes, the code changes to 13 and becomes a full lockout. On this variable-speed furnace the ECM blower keeps running to pull heat off the heat exchanger while the limit is open, which is why you often hear the blower running hard with no burner flame.

The overwhelmingly common root cause is restricted airflow: a clogged filter or closed/blocked supply and return vents. When the blower cannot move enough air across the heat exchanger, temperatures climb until a limit opens. Less commonly, a restricted vent, inadequate combustion air, high wind, or an actual defective limit or rollout switch is responsible. The control auto-resets after three hours, but it will lock out again if the airflow restriction is not removed.

What You'll Notice

• The furnace blows air but the burners shut off and little or no real heat is produced
• The blower keeps running hard, sometimes for long stretches, trying to cool the heat exchanger
• The house drifts cold and the furnace will not restart until the lockout clears or you cycle power
• You may find a very dirty filter or several closed or blocked registers around the home

Common Causes

How This Is Diagnosed

The cause is isolated from the airflow path inward: first the filter condition, then the supply and return registers, then the blower and duct system for restriction. Only after airflow is ruled good does attention move to the limit, rollout, and draft-safeguard switches themselves — including whether a flame rollout switch has tripped and needs manual reset, which is a technician check.

How to Fix It: Restore Airflow: Replace the Filter and Open the 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. Inspect and replace the air filter Pull the filter from the return duct or filter slot. If it is dirty, clogged, or more than about three months old, replace it with the correct size. Make sure the airflow arrow on the new filter points toward the furnace.
3. Open every supply and return vent Walk the house and confirm all supply registers and return grilles are fully open and not blocked by furniture, rugs, or curtains. Closing off too many rooms starves the blower of return air and causes exactly this overheating.
4. Look for obvious blower dust buildup With power off, look at the blower wheel through the access opening. Heavy dust on the blades reduces airflow. Do not disassemble the blower — if it is caked with debris or the wheel looks loose, that is a job for a technician.
5. Restore power and gas, then run a full cycle Turn the gas valve back ON and restore power. The control may take up to three hours to auto-reset, or you can cycle power (off 30 seconds, then on) to clear the lockout. Set the thermostat to call for heat and watch a complete cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 13 returns after you replace the filter and open all the vents
• The flame rollout switch has tripped and requires manual reset (a red reset button on the switch)
• The blower runs slowly, makes unusual noise, or the wheel is loose or heavily fouled
• The furnace keeps overheating despite a clean filter and clear ductwork

✓ Verified against manufacturer service manual — March 2026