Ruud U802VA050317MSA Error Code T013_F: Flame Lost after Established

What Does Code T013_F Mean?

Once the Ruud U802VA has proven ignition, the Bluetooth Communicating IFC keeps watching the burner flame the whole time it runs by reading the rectified flame current from the sensor rod. T013_F is logged when that signal disappears for a moment after flame was already established. The 'T' prefix marks it as a transient fault — the control saw a single dropout and recovered, rather than a sustained failure. It is essentially a warning shot: the flame proving is becoming marginal.

The reason this matters on this board is the escalation path built into it. Each dropout counts. If flame is lost five times within one heat call, the transient T013_F is promoted to the active fault A013_F (Flame Lost after Established, active), and the control declares a one-hour lockout that it reports as the status code A114_F (One-hour Lockout: Flame Lost). So T013_F is the point at which the same underlying problem is cheapest and least disruptive to fix, before the furnace starts locking you out of heat.

The most common cause is a flame sensor rod with enough oxide or scale buildup that its microamp reading dips near the detection threshold and occasionally drops out, even though the burner is still clearly burning. Note that T013_F is a mid-run flame-loss code, unlike A011_F (Failed Ignition), which fires when the burner never establishes flame in the first place. Cleaning the sensor rod is the safe homeowner step; a persistently weak flame from low gas pressure or a partly blocked burner is a technician diagnosis.

What You'll Notice

• The furnace lights and heats normally most of the time, but the contractor app logs an occasional T013_F
• You may notice a brief pause or the blower running slightly longer on some cycles as the control re-checks flame
• Heat is delivered, so the house still warms up — this code often appears before any obvious loss of heating
• Occasionally you may hear the burners cut out and relight within the same cycle
• The fault appears intermittently rather than every cycle, and may not be present when you check

Common Causes

How This Is Diagnosed

Because T013_F is intermittent, diagnosis starts with the most common and easiest cause: the flame sensor rod is cleaned and the furnace is watched over several cycles to see whether the transient dropouts stop. This is the homeowner-safe step. If dropouts continue with a clean rod, the flame itself is suspected of being weak or unstable.

A technician then reads the steady-state flame current in microamps to see how close it sits to the minimum, and checks burner condition and gas manifold pressure for a flame that is physically wavering. Those pressure and burner checks are professional work, not DIY.

How to Fix It: Clean the Flame Sensor

What You'll Need

• Scotch-Brite pad
• 1/4-inch nut driver or small socket set
• Flashlight

Steps

1. Shut off power and gas before you touch anything Turn off power to the Ruud U802VA at the breaker or the furnace power switch, and shut off the gas supply at the manual shutoff valve on the gas line to the furnace. Confirm the furnace is fully off before opening any panel. If you smell gas, leave immediately and call your gas company.
2. Locate and remove the flame sensor Remove the burner-compartment door. The flame sensor is a single metal rod with a white porcelain base, mounted at the end of the burner assembly opposite the igniter, with one wire running to it. Note the wire routing, disconnect the wire, and remove the single retaining screw so you can lift the rod out.
3. Clean the sensor rod Gently clean the flame sensor rod with a Scotch-Brite pad until the metal is dull-bright. Ruud'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.
4. Reinstall and reconnect Set the rod back in its original position, reinstall the retaining screw, and reconnect the sensor wire exactly as it was routed. Make sure the rod does not touch the burner or any metal bracket. Refit the burner door.

When to Call a Professional

Contact a licensed HVAC technician if:

• T013_F keeps appearing after the flame sensor has been cleaned
• The code escalates to A013_F, or the furnace enters the A114_F one-hour lockout
• The burner flame looks yellow, lazy, or visibly wavers instead of burning a steady blue
• Other gas appliances in the home are also acting up, suggesting a gas supply or pressure issue
• The dropouts happen more often over time rather than clearing after cleaning

✓ Verified against manufacturer service manual — March 2026