| Category | Details |
|---|---|
| Difficulty | Intermediate (Requires basic electrical testing) |
| Estimated Time | 30 to 60 Minutes |
| Tools Needed | Multimeter, 5/16″ Nut Driver or Phillips Screwdriver, New Air Filter |
| Estimated Cost | $20 (Filter) to $150 (Professional Switch Replacement) |
Symptoms of Rheem Error 22
When a Rheem furnace throws an Error 22, it doesn’t just sit there quietly; it exhibits very specific behaviors that I’ve seen in the field for decades. First and foremost, you’ll see the diagnostic LED on the control board flashing. Usually, it’s a “2-flash” sequence—two quick blinks followed by a pause. Physically, the most common symptom is that the indoor blower fan will run non-stop. This is a safety feature designed to cool down the heat exchanger as quickly as possible.
⚡ Safety First: Read Before Repairing
Don’t guess the wiring. Get the official PDF to see the exact schematics.
You might also hear the furnace attempt to click on, but the burners will never ignite, or they might ignite for a few seconds and then shut off abruptly. If you happen to be near the vents when this happens, the air coming out will be cold or, at best, lukewarm. In some cases, you might even smell a slight “hot” or dusty odor right before the unit locks out, which is the smell of the heat exchanger reaching its thermal limit.
Technical Explanation of the Fault
In my years under the hood of these machines, I’ve learned that the Main Limit Switch is basically a thermostat acting as a bodyguard. It is a “normally closed” switch, meaning electricity should always be flowing through it. If the temperature inside the furnace cabinet gets too high, a bimetal disc inside the switch warps and breaks the connection (opening the circuit). Here is why that usually happens:
- Restricted Airflow (The #1 Culprit): Think of your furnace like a runner. If you hold their nose and mouth, they’re going to overheat and collapse. If your air filter is packed with dust, or if too many supply vents are closed, the heat produced by the burners has nowhere to go. It sits inside the heat exchanger until the limit switch says “enough” and cuts the power.
- Blower Motor Fatigue: If the blower motor is failing or the capacitor is weak, the fan won’t spin at the correct RPM. If the fan isn’t moving enough air across the heat exchanger, the temperature climbs rapidly. I often see this in older units where the motor bearings are starting to drag.
- Component Wear and Tear: These switches are mechanical. Every time they “trip” and reset, the internal metal disc loses a bit of its integrity. Eventually, a switch can become “weak,” meaning it trips at a much lower temperature than it’s supposed to. At that point, no amount of cleaning will fix it—the part is simply shot.
- Internal Obstructions: Sometimes, a dirty evaporator coil (if you have AC) sits right above the furnace. If that coil is plugged with pet hair or dust, it acts like a wall, trapping heat in the furnace and tripping the Error 22 code.
Troubleshooting & Replacement Instructions
- Kill the Power: I cannot stress this enough. Before you touch a single screw, go to your breaker panel or the furnace’s service switch and turn it OFF. You’re going to be working near high-voltage components, and a “Veteran’s mistake” is thinking you’re too fast to get shocked.
- Inspect the Air Filter: Pull your filter out. If you can’t see light through it, throw it away. A clogged filter is responsible for about 80% of Error 22 calls I get. Try running the furnace briefly without the filter to see if the error clears; if it does, you’ve found your culprit. Just don’t leave it out for more than a few minutes.
- Check the Vents: Walk around your house. Ensure that at least 80% of your supply registers are open and that no large rugs or furniture are covering the return air grilles. Closing too many vents to “save energy” is a myth that actually kills furnaces by causing this exact error.
- Locate and Inspect the Limit Switch: Use your 5/16″ nut driver to remove the upper cabinet door. The Main Limit Switch is usually located right in the center, mounted on the sheet metal of the heat exchanger. It usually has two wires (often yellow or red) attached to it. Look for signs of scorching or melted wire insulation.
- The Continuity Test: This is where the industry wisdom comes in. Pull the two wires off the switch. Set your multimeter to “Ohms” or “Continuity.” Touch the probes to the two terminals on the switch. If the furnace is cool and the meter shows “OL” (Open Line) or no beep, the switch is dead and needs replacement. If it shows 0.00 ohms (a closed circuit), the switch is fine, and your problem is definitely airflow or a faulty blower.
- Replacing the Switch: If the switch is bad, unscrew the two mounting screws. Pull the old switch out and ensure the replacement has the same “L-Rating” (the temperature at which it trips). Slide the new one in, tighten the screws, and reattach the wires.
- Restore Power and Reset: Put the doors back on (the furnace won’t start if the door switch isn’t depressed). Turn the power back on. The error should clear itself, but if it doesn’t, you may need to cycle the thermostat to “Off” and back to “Heat.”
How to Prevent Error 22
If you want to stay out of the attic or crawlspace, you need to respect the airflow. First, **set a calendar reminder** to change your filter every 30 to 90 days depending on your home (pets make a big difference). Don’t buy those ultra-expensive “HEPA” filters that are 4 inches thick unless your system was specifically designed for them; they often restrict air so much they actually trigger Error 22 on perfectly healthy furnaces.
Second, get your **blower motor inspected** every couple of years. A mechanic can check the “amp draw” of the motor to see if it’s working too hard. Finally, consider a **professional duct cleaning** if you’ve recently done home renovations. Drywall dust is a silent killer for furnace limit switches, coating the heat exchanger and acting like an insulating blanket that keeps the heat in instead of letting it reach your living room.
FAQ
Frequently Asked Questions
Can I just jump the wires or bypass the limit switch to get heat tonight?
Absolutely not. I’ve seen houses burn down because someone “jumped” a safety limit. That switch is there for a reason. If you bypass it and the furnace continues to overheat, the heat exchanger can crack, leaking carbon monoxide into your home, or the cabinet can literally catch fire. If the switch is open, find the cause or stay cold until it’s fixed.
Does Error 22 mean I need a new furnace?
Rarely. In most cases, it’s a $20 filter or a $50 part. However, if the error keeps happening and the airflow is fine, it could indicate a cracked heat exchanger, which is a major repair. If you’re clearing the code and it comes back every week, it’s time to call a pro to scope the heat exchanger for safety.
Why does the fan keep blowing if there’s no fire?
That’s the “Post-Purge” or “Limit Trip” logic. The control board thinks the furnace is a molten block of iron, so it runs the fan to dump that heat as fast as possible. It won’t stop until the limit switch cools down and closes the circuit again. If the fan runs for hours and the air is cold, the switch is likely “stuck” open and needs to be replaced.