Carrier 59SC5A Error Code 14: Ignition Lockout

What Does Code 14 Mean?

Code 14 on the Carrier 59SC5A is an Ignition Lockout. The furnace attempted to ignite multiple times and failed, so the control board has locked out the system as a safety measure. It will automatically reset after three hours and try again.

This code is the escalated version of Code 34 (Ignition Proving Failure). After four consecutive unsuccessful ignition attempts at the Code 34 level, the board escalates to this Code 14 lockout. The most common cause is a dirty flame sensor — the small metal rod inside the burner assembly that detects whether a flame is present. When oxide builds up on the sensor, it can no longer reliably detect the flame, causing the board to shut off the gas valve even though the burner did ignite.

Other possible causes include a failed hot surface igniter (the burner never lights at all), a gas supply issue (gas valve turned off or low gas pressure), or a defective gas valve. If you hear the igniter glowing and see a brief flash of flame before the furnace shuts down, the flame sensor is the most likely problem. If you never see or hear ignition at all, the issue may be the igniter or gas supply.

Common Causes

How to Fix It: Clean the Flame Sensor

What You'll Need

• Fine steel wool (0000 grade) or fine emery cloth
• 1/4-inch hex-head or Phillips screwdriver (to remove flame sensor)
• Clean dry cloth
• Flashlight

Steps

1. Turn off power at the breaker and shut off the gas supply valve Locate the circuit breaker for your furnace and flip it to OFF. Find the gas shut-off valve on the gas line leading to the furnace and turn it to the closed position. If you smell gas at any point, leave the house immediately and call your gas company from outside.
2. Locate the flame sensor Open the furnace burner compartment door. The flame sensor is a thin metal rod (usually bent at an angle) mounted near the burner assembly, with a single wire connected to it. On the Carrier 59SC5A, it is typically secured with one hex-head or Phillips screw.
3. Remove the flame sensor Disconnect the wire from the flame sensor by gently pulling the connector off. Remove the mounting screw and carefully pull the sensor out. Handle it gently — the porcelain insulator is fragile.
4. Clean the sensor rod Use fine steel wool (0000 grade) or fine emery cloth to gently rub the metal rod portion of the flame sensor. The goal is to remove the grayish oxide buildup that prevents the sensor from detecting the flame current. Rub until the metal is shiny. Do not touch the porcelain insulator. Some HVAC professionals recommend using a Scotch-Brite pad instead to avoid residue. Wipe the rod clean with a dry cloth when finished.
5. Reinstall the flame sensor Insert the sensor back into its mounting hole and secure it with the screw. Reconnect the wire connector — it should push on firmly. Make sure the sensor rod extends into the flame path of the burner.
6. Restore power and test Turn the gas supply back on, then turn on the breaker. Set the thermostat to call for heat. The furnace should go through its normal startup sequence: inducer motor starts, igniter glows, gas valve opens, and flame establishes. The flame should stay lit and the blower should start after a short delay.

When to Call a Professional

Contact a licensed HVAC technician if:

• Cleaning the flame sensor does not resolve the issue after 2-3 heating cycles
• The igniter does not glow at all during the startup sequence
• You hear the gas valve click but no flame appears
• The flame ignites briefly but goes out repeatedly despite a clean sensor
• You smell gas near the furnace (leave immediately and call the gas company)