Ruud U802VA050317MSA Error Code A011_F: Failed Ignition

What Does Code A011_F Mean?

Every heat call on the Ruud U802VA runs through a fixed proving sequence on the Bluetooth Communicating IFC: the inducer starts and proves draft through the pressure switch, the hot-surface igniter glows, the gas valve opens, and the flame sensor rod must return a small rectified flame-current signal within the trial-for-ignition window. A011_F is the control's verdict that this signal never arrived on any of four consecutive trials. After the fourth failed trial the IFC stops trying and enters a one-hour lockout, which it reports separately as A113_F One-hour Lockout: Ignition Failure.

Because this control proves flame by electrical rectification through the sensor rod, a burner that actually lights but is not "seen" produces the same A011_F as a burner that never lit at all. That is why a dirty or lightly corroded flame sensor is a frequent culprit: a film of oxide or scale on the rod chokes the microamp signal below the IFC's detection threshold, the control assumes ignition failed, and it closes the gas valve within a couple of seconds even though flame was briefly present. The other common causes on this platform are a weak hot-surface igniter that no longer reaches ignition temperature and an interrupted gas supply.

A011_F is distinct from the flame-loss codes on the same board. T013_F (Flame Lost after Established, a transient/intermittent flame loss) and its active escalation A013_F (flame lost five times in one heat call) apply when flame was proven and then dropped mid-run; A011_F applies only when flame was never established in the first place. If instead the IFC sees the gas valve energized but still senses no flame at the UL safety level, it logs A126_F (Flame not Sensed with Gas Valve On). Cleaning the flame sensor is the one safe, homeowner-appropriate step here; anything touching the igniter, gas valve, or gas pressure belongs to a technician.

What You'll Notice

• The furnace runs the inducer and the igniter glows, you may hear the gas valve click, but the burners either never light or light for only a second before shutting off
• The blower may push cool or barely-warm air and the house does not reach the thermostat setpoint
• After four attempts the furnace goes silent and will not retry for about an hour (the paired A113_F lockout)
• The contractor app shows A011_F as an active fault after the ignition sequence fails
• You may hear the ignition sequence repeat several times in a row before it stops

Common Causes

How This Is Diagnosed

The cause is isolated by working along the same order the IFC uses. The flame sensor is checked first, because a rod coated with oxide is the cheapest and most common reason a lit burner reads as "no flame" — this is the part a homeowner can clean. If the burners clearly never ignite at all, attention shifts to whether the hot-surface igniter is glowing and reaching temperature, then to whether gas is actually reaching the valve (manual shutoff open, LP tank not empty, upstream valves open).

A technician confirms the diagnosis by reading the flame-current microamps while the burner is lit and comparing it to the manufacturer's minimum, and by measuring igniter resistance and gas manifold pressure. Those measurement steps involve the gas valve and the live burner and are 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:

• The burners clearly never light at all, which points to the igniter or gas supply rather than the flame sensor
• A011_F returns after the flame sensor has been cleaned and reinstalled correctly
• The igniter is not glowing, or it glows only dimly
• Nearby gas appliances are also starved or the gas has been recently interrupted, suggesting a supply or pressure problem
• The furnace re-locks out (A113_F) repeatedly even though it briefly lights

✓ Verified against manufacturer service manual — March 2026