Ruud U802VA050317MSA Error Code T022_F: Main Limit Switch Open (Transient)
What Does Code T022_F Mean?
Code T022_F on the Ruud U802VA indicates that the main high-temperature limit switch opened because the furnace reached an unsafe internal temperature. The 'T' prefix means this is a transient (intermittent) occurrence — the overheat happened but may have cleared on its own as the blower cooled things down.
The limit switch is a safety device mounted on the heat exchanger or plenum. When the air temperature inside the furnace exceeds a safe threshold, the switch opens and cuts off the gas burners. The blower continues running to cool the heat exchanger. Once the temperature drops, the limit switch closes and the furnace may attempt to restart.
The most common cause is insufficient airflow through the furnace, usually due to a dirty or clogged air filter. Blocked or closed supply registers and return air grilles can also restrict airflow enough to cause overheating. If all vents and filters are clean, a blower motor that is running too slow or a ductwork problem may be responsible.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Dirty air filter restricting airflow | Most common | ✓ DIY fix → |
| Blocked or closed supply registers | Common | ✓ DIY fix → |
| Blower motor failure | Uncommon | ✗ Call a pro → |
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 the filter is visibly dirty, gray, or has not been replaced in over 3 months, replace it with a new filter of the correct size. 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 in your home and ensure all supply registers and return air grilles are fully open. Move any furniture, curtains, or rugs that may be blocking airflow. Even a few closed or blocked vents can significantly restrict airflow and cause the furnace to overheat.
- Inspect the area around the furnace Make sure nothing is stored against or on top of the furnace that could block airflow to the blower compartment. Check that the blower access panel is properly seated — a loose panel can disrupt airflow.
- Restore gas and power, then test Turn the gas supply valve to ON and restore electrical power. Set your thermostat to call for heat and monitor the furnace through a complete heating cycle. Listen for the blower motor running at normal speed.
When to Call a Professional
Contact a licensed HVAC technician if:
- Code T022_F returns after replacing the filter and opening all vents
- The blower motor sounds weak, makes unusual noises, or does not run at all
- You notice the furnace frequently cycling on and off (short cycling)
- The problem occurs even with a brand-new filter installed
- You suspect ductwork may be collapsed or disconnected
Sources
✓ Verified against manufacturer service manual — March 2026