Ruud U96VA0702317MSA Error Code 13: Flame Lost After Established

What Does Code 13 Mean?

Code 13 on the Ruud U96VA0702317MSA means the integrated furnace control (IFC) board successfully detected a flame at startup but then lost the flame signal while the thermostat was still calling for heat. This is distinct from a failure to ignite in the first place — the burners did light, but combustion stopped before the heating cycle was complete. The IFC will retry a limited number of times before locking out and displaying the fault code.

The flame sensor is the first thing to investigate. This small metal rod sits in the burner flame and conducts a tiny electrical current back to the control board to confirm ongoing combustion. When oxide or carbon deposits build up on the rod, the current weakens. Code 12 (low flame signal) often appears first as a warning; if the buildup continues, the signal eventually drops below the IFC's threshold entirely, causing the flame to be considered lost — that is code 13. Cleaning the flame sensor rod resolves the majority of these faults. A dirty or misaligned rod, an intermittent gas supply issue (low gas pressure, a partially closed shutoff valve), or a weak flame caused by a dirty burner are all possible contributors.

When to call a professional: if the fault returns after cleaning the flame sensor, or if you notice the burners producing an uneven, yellow, or lazy flame, the problem is likely beyond a simple cleaning. Gas pressure should only be measured and adjusted by a licensed technician. If the furnace has been short-cycling repeatedly before this code appeared, or if you smell gas at any time, do not attempt a DIY repair — shut off the gas and call a technician.

Common Causes

How to Fix It: Clean the Flame Sensor

What You'll Need

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

Steps

1. Shut off power at the breaker and close the gas supply valve Flip the furnace circuit breaker to the OFF position. Turn the manual gas shutoff valve near the furnace so the handle is perpendicular to the gas pipe. If you smell gas at any point during this process, leave the house immediately and call your gas company from outside.
2. Remove the furnace access panel Remove the front access panel on the U96VA to expose the burner assembly. The panel may be secured with screws or spring clips. Set it aside in a safe location.
3. Locate and remove the flame sensor The flame sensor is a thin metal rod attached to a porcelain insulator, mounted near the burner with a single mounting screw. It has one wire connected to it. Disconnect the wire and remove the screw, then carefully pull the sensor free.
4. Clean the sensor rod Gently rub the metal rod portion with a Scotch-Brite pad until all dark oxide or carbon buildup is removed and the metal looks clean. Do not use steel wool, as it can leave conductive residue. Avoid bending the rod or chipping the porcelain insulator.
5. Reinstall the sensor and reconnect the wire Slide the sensor back into its bracket, tighten the mounting screw snugly, and reconnect the wire connector. Confirm the rod will extend into the burner flame path when the burners are lit.
6. Restore power and gas, then run a test cycle Open the gas shutoff valve (handle parallel to the pipe) and flip the circuit breaker back ON. Set the thermostat above room temperature to call for heat. Let the furnace complete a full heating cycle — the burners should stay lit until the thermostat is satisfied. Watch for the code to clear on the next successful cycle.

When to Call a Professional

Contact a licensed HVAC technician if:

• Code 13 returns after cleaning the flame sensor — the sensor itself may need replacement
• The burners produce a yellow, weak, or uneven flame, which can indicate a dirty burner or low gas pressure
• Gas pressure needs to be checked or adjusted — this requires a manometer and must be done by a licensed technician
• The fault escalates to a lockout (multiple retries without a successful cycle)
• You smell gas at any point during inspection or operation
• You are not comfortable shutting off gas or disassembling furnace components

✓ Verified against manufacturer service manual — March 2026