Ruud U802VA050317MSA Error Code A011_F: Failed Ignition

What Does Code A011_F Mean?

Code A011_F on the Ruud U802VA means the furnace attempted to light the burners four times and could not confirm a flame was present, so it shut down for safety. Each time the control tries to ignite, the inducer motor runs to prove draft, the hot surface igniter heats up, the gas valve opens, and the flame sensor looks for flame. If the sensor does not detect a flame signal within the trial period, the gas valve closes and the control counts one failed attempt. After four consecutive failures, code A011_F is set.

A dirty flame sensor is the single most common homeowner-fixable cause. The sensor detects flame by passing a tiny electrical current through the flame; even a thin layer of oxidation on the sensor rod is enough to block that current and make the control think no flame exists — even when the burners did light briefly. A worn-out hot surface igniter that no longer reaches ignition temperature is another frequent cause, though that part is best replaced by a technician. Gas supply issues (a closed shutoff valve, very low gas pressure, or an empty tank on propane systems) are also worth ruling out before calling for service.

If this code recurs, the furnace enters a one-hour safety lockout recorded as code A113_F. The lockout period lets the system cool and prevents continuous gas cycling. After one hour, the control will automatically try again — but if the underlying problem is not fixed, A011_F will trigger again and a new lockout will begin.

Common Causes

How to Fix It: Clean the Flame Sensor

What You'll Need

• Scotch-Brite pad
• 1/4-inch hex-head nut driver or screwdriver
• Flashlight
• Clean cloth or paper towel

Steps

1. Turn off electrical power at the breaker or power switch AND shut off the gas supply valve Locate the furnace circuit breaker and flip it to OFF, or use the dedicated power switch on or near the furnace. Turn the gas shutoff valve to the OFF position (handle perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company — do not continue this procedure.
2. Open the furnace access panel and locate the flame sensor Remove the furnace's front access panel. The flame sensor is a thin metal rod with a porcelain insulator at its base, mounted near the burners. On Ruud U802VA models it is secured by a single mounting screw and extends into the burner flame path.
3. Remove and clean the flame sensor Disconnect the wire connector from the sensor and remove the mounting screw. Gently rub the metal rod with a Scotch-Brite pad until the surface is clean and shiny. Wipe the rod clean with a dry cloth before reinstalling.
4. Inspect the hot surface igniter While the access panel is off, visually inspect the hot surface igniter — a small ceramic or silicon nitride element positioned near the burner orifices. Look for visible cracks or a broken element. If the igniter is cracked, it will not reach ignition temperature and needs replacement by a technician. Do not touch the igniter surface with bare hands, as skin oils can cause premature failure.
5. Verify the gas supply is turned on Confirm the manual gas shutoff valve near the furnace is in the ON position (handle parallel to the pipe). Also check that any upstream shutoff valves in the gas line are open. A valve accidentally left in the OFF position is a simple but easily overlooked cause of ignition failure.
6. Reinstall the flame sensor and restore power Reattach the flame sensor with its mounting screw, reconnect the wire connector, and replace the access panel. Turn the gas valve back to ON and restore electrical power. To clear the lockout, cycle power (turn it off for 30 seconds, then back on). Set the thermostat to call for heat and observe whether the furnace ignites successfully.

When to Call a Professional

Contact a licensed HVAC technician if:

• The furnace still fails to ignite after cleaning the flame sensor
• The igniter does not glow red-orange when the furnace attempts to light
• The igniter is visibly cracked or broken
• You can hear the gas valve click but see no flame at the burners
• You smell gas near the furnace — leave the area immediately and call your gas company
• Code A011_F keeps recurring, triggering repeated code A113_F lockouts

✓ Verified against manufacturer service manual — March 2026