Bryant Furnace Limit Circuit Lockout – Meaning, Causes & Fix

What Does Limit Circuit Lockout Mean?

What Causes This Error?

• Dirty or clogged air filter severely reducing airflow across the heat exchanger — the most common cause, repeated across cycles
• Closed or blocked supply registers reducing total system airflow and causing repeated overheating
• Blocked or collapsed return air duct starving the blower of air
• Failed blower motor, bad blower capacitor, or failed blower control board — no air moves across the heat exchanger
• Dirty blower wheel clogged with dust and debris, unable to move enough air
• Oversized furnace short-cycling and overheating the heat exchanger on short cycles
• Cracked heat exchanger causing abnormal airflow patterns and repeated overheating — a serious safety issue posing a carbon monoxide risk
• Faulty limit switch tripping open at a temperature below its set point, causing repeated false trips

How to Fix Limit Circuit Lockout

1. 1

   Turn off power to the furnace and replace the air filter. At the breaker or furnace disconnect, turn off power to the furnace. Locate the air filter (typically in the return air duct or blower compartment), check its condition, and replace it with a clean filter of the correct size if it's dirty. A dirty filter is the most common cause of limit circuit lockout.

2. 2

   Open all supply and return registers. Walk through the home and confirm all supply registers are open and unobstructed (not covered by furniture, rugs, or curtains), and that all return grilles are clear. Closing registers to save energy is a common cause of furnace overheating.

3. 3

   Reset the furnace by power-cycling. With the air filter replaced and registers open, leave the furnace power off for 60 seconds to clear the lockout state, then restore power at the breaker or furnace disconnect. Set the thermostat to call for heat and observe a full heating cycle.

4. 4

   Observe whether the lockout recurs across multiple cycles. If the furnace completes one heating cycle but locks out again on a subsequent cycle, the overheating cause is persistent and hasn't been resolved by the filter and register checks — proceed to blower diagnosis.

5. 5

   Verify the blower motor runs during the heating cycle. With power on and a heat call active, confirm the blower motor starts and runs smoothly at the correct speed. If the blower doesn't start, hums, or runs slowly, the blower motor, blower capacitor, or blower control board has failed and needs replacement.

6. 6

   Call a licensed HVAC technician if the lockout recurs. If the limit circuit lockout returns after replacing the filter, opening all registers, power-cycling, and confirming the blower runs, call a licensed HVAC technician. The cause is likely a failed blower, a dirty blower wheel needing professional cleaning, a faulty limit switch, an oversized furnace, or a cracked heat exchanger — all requiring professional diagnosis, and a cracked heat exchanger poses a carbon monoxide risk.

When to Call a Professional

Can You Still Use the Device?

A Bryant furnace in limit circuit lockout will not produce heat — the control board has locked out the entire heating system and will not attempt another heating cycle until it is manually reset (by power-cycling at the breaker or furnace disconnect). The furnace's blower may run continuously (in a cool-down or fault mode), but no heat will be produced. Heating calls will not be fulfilled until the underlying overheating condition is resolved and the furnace is reset.