Ruud U802VA050317MSA Error Code A111_F: One-hour Lockout: Main Limit Switch
What Does Code A111_F Mean?
Code A111_F on the Ruud U802VA indicates that the furnace has entered a one-hour safety lockout due to repeated main limit switch trips. The control detected that the main limit circuit was open for more than 150 seconds, which is classified as a 'dead blower' condition — the blower motor is not moving enough air to keep the furnace from overheating.
This code is the lockout status that results from persistent overheating (related to codes T022_F and A022_F). The furnace will not attempt another heating cycle until the one-hour lockout expires or power is cycled after the problem is resolved.
The most common DIY-fixable cause is severely restricted airflow — a clogged air filter, closed vents, or blocked return air grilles. However, because this lockout is triggered by the 150-second dead blower threshold, there is a significant possibility that the blower motor itself has failed or is running too slowly. Check the filter and vents first, but be prepared to call a technician if the blower motor is the problem.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Blower motor not running (dead blower) | Most common | ✗ Call a pro → |
| Severely restricted airflow | Common | ✓ DIY fix → |
How to Fix It: Replace the Air Filter and Restore Airflow
What You'll Need
- Replacement air filter (correct size for your system) 🛒 Find at FiltersFast · 🛒 Find at Amazon
- Flashlight
Steps
- 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 power switch on or near the furnace. Turn the gas shutoff valve to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave the area immediately and call your gas company.
- Check and replace the air filter Remove the air filter from the return air duct or furnace filter slot. If it is dirty, clogged, or has not been changed recently, replace it with a new filter of the correct size. A severely clogged filter can restrict airflow enough to trigger the dead blower detection. Make sure the airflow direction arrow on the new filter points toward the furnace.
- Verify all supply and return vents are open Walk through every room and ensure all supply registers and return air grilles are fully open and not blocked by furniture, curtains, or rugs. Even a few blocked vents can restrict airflow significantly.
- Check whether the blower motor runs Restore power temporarily and set the thermostat fan to ON (continuous fan mode, not AUTO). Listen for the blower motor. If you hear it running at normal speed, the motor is working and the problem was likely the filter/vents. If the motor does not run, hums without spinning, or sounds weak, the motor or its capacitor has likely failed — this requires professional repair.
- Restore gas and power, then test If the blower motor runs normally, turn the gas supply valve to ON and restore full power. Cycle the power (off for 30 seconds, then back on) to clear the lockout. Set the thermostat to call for heat and monitor the furnace through a complete cycle.
When to Call a Professional
Contact a licensed HVAC technician if:
- The blower motor does not run or makes abnormal noises (humming, grinding)
- Code A111_F returns after replacing the filter and opening all vents
- The furnace repeatedly overheats even with a clean filter and open vents
- You feel very little airflow from the supply vents even when the blower is running
- The furnace has tripped this lockout more than once
Sources
✓ Verified against manufacturer service manual — March 2026