Carrier 59TN6 Furnace Problems & Error Codes — Overview
The Carrier 59TN6 is a residential gas furnace that uses an LED fault code system on the control board to signal operating problems. Code 33, indicating an open limit switch or flame rollout switch lockout, is the most frequently reported fault and nearly always traces back to airflow restriction or overheating. The furnace shuts down and locks out when the high-limit safety opens from excess heat or when a rollout switch detects flame spillage. Most Code 33 calls are resolved by correcting airflow problems like plugged filters, dirty blower wheels, blocked return grilles, or duct restrictions. Less commonly, the limit switch itself fails open or wiring in the limit circuit becomes damaged.
Most Common Problems on This Model
- Code 33: Open limit switch or flame rollout switch lockout Caused by restricted airflow (dirty filter, plugged blower wheel, blocked ducts) that allows the heat exchanger to overheat and trip the limit switch, or by combustion problems that open the flame rollout switch.
- Furnace cycles on limit switch without lockout code Poor airflow from a clogged filter, dirty blower wheel, or undersized ductwork causes the limit to open and close repeatedly, shutting off the burners before the thermostat is satisfied.
- Blower runs but burners won’t ignite Control board faults (ignition lockout codes) or failed igniter, flame sensor, or gas valve prevent burner light-off after the inducer and blower start.
- Weak or no airflow from registers A dirty or obstructed blower wheel, failed blower motor, or blocked supply ducts reduce or eliminate heated air delivery even when the blower is running.
- Flame rollout switch opens or shows signs of flame spillage Blocked flue or vent, failed inducer motor, cracked heat exchanger, or improper combustion air supply causes flames to roll out of the burner box and trip the rollout switch.
- Furnace locks out with no or intermittent LED code Loose or corroded wiring at the control board, limit switch, or rollout switch terminals creates open circuits that the board reads as a safety fault.
- Furnace won’t stay running after manual reset Underlying airflow, venting, or component problem (dirty filter, plugged vent, failed limit or rollout switch) causes repeated safety trips and lockouts even after clearing the code.
- Noisy blower or rattling during heating cycle Debris or dirt buildup on the blower wheel or a failing blower motor bearing causes vibration, noise, and reduced airflow that can lead to limit trips.
Parts That Commonly Fail
| Part | Notes |
|---|---|
| Limit switch | Amazon | Opens on overheating from airflow restriction or fails open with age; part of the Code 33 limit circuit. |
| Flame rollout switch | Amazon | Trips when flame spillage is detected; also part of the Code 33 fault path and must be inspected for cause before reset. |
| Blower motor or blower wheel | Amazon | Dirty wheel or motor failure reduces airflow and causes limit switch trips; cleaning or replacement restores proper operation. |
| Control board | Amazon | Replace only after verifying all field wiring, switches, and voltages are correct; board misreads or cannot process limit circuit in rare cases. |
When to Call a Pro
Call a licensed HVAC technician for any gas furnace lockout code, especially Code 33 or flame rollout faults, because these indicate overheating or combustion safety problems. A pro will diagnose the root cause (airflow, venting, or failed component), test limit and rollout switches for proper operation, inspect the heat exchanger and flue for blockages or cracks, and verify safe combustion before clearing the lockout. All gas valve work, combustion analysis, heat exchanger inspection, and venting diagnostics require a qualified technician with proper tools and training. If you see soot, smell gas, or observe flames outside the burner box, shut off the furnace immediately and call for service.