Carrier 59SC5A Error Code 14: Ignition Lockout

What Does Code 14 Mean?

Status code 14 on the Carrier 59SC5A is an ignition lockout. The furnace tried to ignite, could not confirm a flame across its attempts, and has shut down for safety. The HK42FZ036 control will auto-reset after three hours.

Code 14 is the lockout that code 34 becomes. During a heat call the inducer runs, the pressure switch proves draft, the hot surface igniter glows, the gas valve opens, and the flame sensor must confirm combustion. Each failed proof is flagged as code 34; after three additional failed retries the board latches into this lockout, code 14. So a code 14 almost always means the code 34 condition behind it was never resolved.

The most common cause is a dirty flame sensor coated with oxide, which drops the sensing current below the level the board needs to confirm flame, even when gas is actually burning. The next most common is the gas supply being shut off at a manual valve. A defective hot surface igniter or low gas pressure are also possible but typically require professional diagnosis. Cleaning the flame sensor and confirming the gas is on resolves most code 14 events.

What You'll Notice

• The furnace is locked out with no heat and code 14 is flashing
• You may have seen the furnace attempt to light several times, then give up, before it locked out
• The igniter may glow and gas may briefly ignite, but the flame is not sustained
• There is no heat at all if the manual gas valve was left closed
• The furnace stays off for up to three hours before trying again on its own

Common Causes

How to Fix It: Clean the Flame Sensor and Confirm Gas Supply

What You'll Need

• 1/4-inch hex head driver or nut driver
• Scotch-Brite pad
• Flashlight

Steps

1. Turn off electrical power at the breaker and shut off the gas supply valve Flip the furnace circuit breaker to OFF and turn the manual gas shutoff valve to the OFF position (handle perpendicular to the pipe). If you smell gas, leave immediately and call your gas company.
2. Locate the flame sensor Open the furnace access panel and look near the burner assembly. The flame sensor is a thin metal rod, usually bent at an angle, mounted on a white porcelain insulator with a single wire and held by one 1/4-inch screw.
3. Remove the flame sensor Disconnect the wire, remove the mounting screw, and carefully withdraw the sensor. Handle it by the porcelain insulator or bracket, not the rod.
4. Clean the sensor rod Gently clean the flame sensor rod with a Scotch-Brite pad until the metal is dull-bright. Carrier's guide lists fine steel wool as the cleaning material, but many HVAC technicians prefer a Scotch-Brite pad because it leaves no abrasive residue on the rod. Do not clean or scratch the white porcelain base, and take care not to bend the rod.
5. Reinstall the flame sensor Seat the sensor back in its bracket, secure the screw, and reconnect the wire, making sure the rod will sit in the flame path when the burners light. Confirm the green/yellow ground wire stays connected to the furnace sheet metal so the sensor is grounded correctly.
6. Confirm the gas supply is on Check that the manual gas shutoff valve at the furnace is open (handle parallel to the pipe), and that any other manual valve in the gas line is open.
7. Restore power and gas, then test Turn the gas valve to ON and the breaker to ON. Set the thermostat to call for heat and watch the full ignition sequence. The furnace may need a power cycle (off 30 seconds, then on) to clear the lockout.

When to Call a Professional

Contact a licensed HVAC technician if:

• The burners still fail to stay lit after cleaning the flame sensor and confirming gas is on
• The hot surface igniter does not glow during the ignition sequence
• You can hear gas but it does not ignite, or ignition is rough or delayed
• The flame looks yellow or lazy, or flame rolls out of the burner box
• Code 14 keeps returning even with a clean sensor and an open gas supply

✓ Verified against manufacturer service manual — March 2026