Ruud U96VA0702317MSA Error Code 22: Main Limit Open

What Does Code 22 Mean?

Code 22 on the Ruud U96VA0702317MSA means the main high-temperature limit switch has opened — the temperature in the heat-exchanger area rose above its safe threshold, so the Integrated Furnace Control stops gas heating until things cool down. Cooling and fan modes still work. This is a critical fault because it protects the heat exchanger from overheating.

Overheating on a furnace almost always means not enough air is moving across the heat exchanger. On this variable-speed model that usually points back to airflow restriction — a dirty filter or blocked ductwork — rather than the burner. If the limit stays open for more than 150 seconds, the control declares a dead (non-operational) blower and proceeds to a one-hour lockout, where code 22 or code 61 alternates with code 10.

The most common cause is a clogged air filter, which is a homeowner-safe first check. Other causes — a failing blower motor (see code 61), a faulty limit switch, loose wiring, or an input rate set too high — require a technician.

What You'll Notice

• The furnace heats for a while, then shuts off on high temperature before the thermostat is satisfied
• Registers blow warm then cool as the burners cut out but the blower keeps running
• A visibly dirty or clogged air filter, or closed/blocked supply and return vents
• Repeated tripping can escalate to a lockout with code 22 or 61 alternating with 10

Common Causes

How This Is Diagnosed

The first and easiest check is airflow: inspect the air filter and make sure supply and return vents are open and unobstructed, since restricted airflow is the most common cause of an overheating limit trip.

If airflow is clear, the technician measures external static pressure, checks the blower motor operation (cross-referencing code 61 for a dead blower), and tests the limit control and its wiring; they also confirm the furnace input rate and burner orifices are correct for the installation.

How to Fix It: Check and Replace the Air Filter

What You'll Need

• Replacement furnace filter (correct size) 🛒 Find at FiltersFast · 🛒 Find at Amazon
• Flashlight

Steps

1. Turn off power at the breaker or switch and shut off the gas supply Switch off the furnace at its dedicated breaker or the service switch on the unit, then turn the manual gas shutoff valve near the furnace to the OFF position (handle crosswise to the pipe). If you smell gas, leave immediately and call your gas company. Give the unit a minute for the inducer to stop before opening any panels.
2. Locate the air filter Find the filter in the return-air slot or filter cabinet at the furnace, or behind a return-air grille. Note the size printed on the frame before removing it.
3. Remove and inspect the filter Slide the filter out and hold it up to a light. If you cannot see light through it, or it is gray with dust, it is restricting airflow and should be replaced.
4. Install a clean filter facing the right way Insert a new filter of the same size, following the airflow arrow on the frame so it points toward the furnace/blower. A crushed or wrong-size filter can leak air and still cause overheating.
5. Open and clear the vents Make sure supply registers and return-air grilles throughout the home are open and not blocked by furniture, rugs, or closed doors, so the blower can move enough air.
6. Restore power and gas, then let it cool and test Restore power and reopen the gas supply. The limit may need time to cool before it resets; set the thermostat to call for heat and confirm the furnace completes a full cycle. A power cycle may be needed to clear the code.

When to Call a Professional

Contact a licensed HVAC technician if:

• The furnace still overheats after the filter is replaced and vents are confirmed open
• The blower does not run or seems weak, or the code pairs with 61 (dead blower)
• The limit reaches a one-hour lockout (code 22 or 61 alternating with 10)
• You suspect the furnace input rate is set too high or the limit switch itself is faulty

✓ Verified against manufacturer service manual — March 2026