Ruud U802VA050317MSA Error Code A111_F: One-hour Lockout: Main Limit Switch

What Does Code A111_F Mean?

A111_F is not a new failure so much as the end state of the overheat chain on the Ruud U802VA's Bluetooth Communicating IFC. The main high-limit switch opened, the control found the limit circuit open for more than 150 seconds and declared a 'dead blower', and after that pattern the board placed the furnace into a one-hour lockout so it stops re-igniting into an overheating heat exchanger. During the lockout the control will not start a heat cycle at all — the furnace simply waits.

Understanding how you arrived here helps target the fix. The same overheat condition shows up transiently as T022_F (limit briefly opened and reclosed), actively as A022_F (limit staying open right now), and finally as A111_F once the control commits to the one-hour main-limit lockout. All three describe the furnace being unable to shed the heat the burners produce. The 150-second dead-blower threshold that triggers this lockout is the tell: it means the control believes the blower is not moving air, which is closely related to the A061_F 'Blower Fault - Motor Cannot Run' hard lockout.

Because the U802VA is a variable-speed furnace, the ECM blower is supposed to ramp up automatically to carry heat away as the burners fire. When A111_F is set, either that motor is not running or airflow is so restricted that the heat exchanger overheats anyway. You can clear the lockout by cycling power, but if you have not fixed the airflow or blower problem it will simply overheat and lock out again. The homeowner-safe move is to rule out a severely clogged filter and blocked returns; if the code returns, the blower is the likely cause and that is professional work.

What You'll Notice

• The furnace is completely idle and will not respond to a heat call for up to an hour — no burner ignition, no blower.
• Right before the lockout, the furnace was short-cycling: lighting briefly, then shutting the burners off on the limit.
• The house temperature has dropped noticeably because no heat cycles are completing.
• The contractor app shows A111_F along with earlier T022_F/A022_F main-limit trips and a dead-blower entry.
• After the hour expires (or after you cycle power), the furnace tries again but locks out once more if the cause is unresolved.

Common Causes

How This Is Diagnosed

Diagnosis works backward from the lockout: the technician reviews the fault history to confirm the main-limit trips and the 150-second dead-blower declaration that caused A111_F, then determines whether airflow or the blower itself is at fault. Airflow items (filter, returns, supplies) are ruled out first because they are quick and homeowner-safe. If airflow is adequate and the lockout recurs, the ECM blower motor, its control module, capacitor, and wiring are checked in that order — that verification is technician work, since the dead-blower trigger points at a motor that will not run.

How to Fix It: Clear the lockout and rule out the one homeowner-safe cause (restricted airflow)

What You'll Need

• Replacement furnace air filter (correct size, printed on the old filter's frame) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Shut off power and gas first Turn off power to the Ruud U802VA at the breaker or the furnace switch, and shut off the gas supply valve at the furnace. If you smell gas, leave immediately and call your gas company. Do not continue until both power and gas are off.
2. Replace a clogged filter Pull the filter and hold it to a light. If it is heavily loaded, install a new one of the same size shown on the frame. A severely restricted filter is the only overheat cause a homeowner should address here — and on an A111_F lockout it frequently will NOT clear the code, because the control detected a dead blower.
3. Open all registers and return grilles Confirm every supply register is open and no return grille is blocked by furniture, rugs, or drapes, so the blower has a clear path to carry heat away from the heat exchanger.
4. Restore gas and power to clear the lockout, then watch one cycle Turn gas back on and restore power; cycling power resets the one-hour lockout so the furnace can try again immediately. Watch the blower closely: if it does not spin up when the burners try to light, or A111_F/A022_F returns within minutes, stop and call a technician — the blower is not moving air and this is not a homeowner repair.

When to Call a Professional

Contact a licensed HVAC technician if:

• A111_F returns after you cycle power, replace the filter, and confirm all vents are open.
• The blower does not spin up, runs very slowly, or is silent when the furnace calls for heat.
• The fault history shows a dead-blower declaration or an A061_F blower hard lockout alongside the main-limit trips.
• You smell a hot or burning odor, or the furnace repeatedly short-cycles on the limit before locking out.

✓ Verified against manufacturer service manual — March 2026