What to Do When Your Radon Fan Is Not Working: A Homeowner's Guide

If you own a home with a radon mitigation system, the fan is the heart of the operation. It pulls soil gas from beneath your foundation and vents it safely above the roofline. When that fan stops, the whole system goes quiet, and radon levels can climb back up within hours. I have seen this happen more times than I can count, and it always catches homeowners off guard. The good news is that a radon fan not working is usually something you can diagnose quickly, and often fix without replacing the whole system.

In St. Louis, where I work with Air Sense Environmental on radon system repair and fan replacement, the most common call we get is about a fan that has suddenly gone silent. It might be a RadonAway unit that has run for years without issue, or a newer GP-201 that never seemed quite right from the start. Whatever the brand, the troubleshooting steps are largely the same. Let me walk you through what I check first when a homeowner tells me their radon fan has stopped.

Start With the Basics: Power and Connections

Before you assume the fan motor has failed, look at the power supply. A circuit breaker that tripped is one of the simplest causes of a radon fan not working, and it happens more often than you might think. If your system shares a circuit with a sump pump, a dehumidifier, or even a heat recovery ventilator, a surge can knock the fan off line. Reset the breaker and see if the fan comes back. If it does, you have saved yourself a service call.

Next, check the disconnect switch. Many installations include a switch near the fan unit itself, sometimes inside the attic or crawlspace. If someone bumped it or flipped it off during maintenance, the fan will not run. I have driven across St. Louis only to find a disconnect switch in the off position. It happens. Also inspect the fan controller if your system has one. Some controllers have a built-in thermal cutout that can trip if the fan gets too hot. Let it cool for an hour and try again.

Listen and Look for Clues

If power is present and the fan still will not run, listen closely. A humming fan that does not spin usually points to a bad capacitor. The capacitor gives the motor the extra torque it needs to start turning. When it fails, you hear a hum but no movement. This is a common failure on older RadonAway models and on the RN101 series. Replacing a capacitor is a straightforward repair for a technician, but it is not a DIY job unless you are comfortable working with electrical components.

If you hear nothing at all, the motor may have seized, or the fan leads could have come loose. Vibration from years of running can loosen wire connections inside the junction box. I have opened up fans where a single wire nut had backed off just enough to break contact. Tightening the connections fixed the problem in under a minute. But if the motor is truly seized, usually from moisture or debris getting inside the housing, replacement is the only option.

Check Airflow and Pressure

A fan that runs but does not move air is another variation of a radon fan not working. This can happen if the PVC piping is blocked or if the fan impeller is damaged. Use a manometer to measure the pressure difference across the fan. A healthy sub-slab depressurization system typically reads between 0.5 and 1.5 inches of water column. If you see zero or a very low reading, the fan may be spinning but not creating the laminar flow needed to pull soil gas.

A pitot tube can help you check airflow velocity in the main vent pipe. If the velocity is low despite the fan running, look for a blockage. I once found a bird nest in the vent pipe of a home in south St. Louis. The fan was running fine, but the nest was choking the airflow. Clearing the pipe restored the system to full function. Also check the Radon Seal around the pipe entry points. A broken seal can let outside air in, reducing the vacuum and making the fan work harder without moving much soil gas.

When to Call a Professional

Some problems are beyond what a homeowner should tackle. If you have checked the breaker, the disconnect switch, and the fan controller, and the fan still will not run, it is time to call someone who does this every day. In St. Louis, Air Sense Environmental handles exactly this kind of repair. They can test the capacitor, check the fan leads, and determine if a full fan replacement is needed. They also carry parts for RadonAway, GP-201, and RN101 fans, so you are not waiting weeks for a backordered component.

Another reason to call a pro is safety. Working on electrical components in a damp crawlspace or attic carries risks. And if the fan has failed due to moisture intrusion, there may be mold or corrosion that needs attention. A technician can also verify that the rest of the system, including the PVC piping and the Radon Seal, is intact. A simple fan repair can turn into a bigger job if the underlying cause is a cracked pipe or a compromised seal.

What Happens While the Fan Is Down

While you wait for a repair, your radon levels can rise. The EPA recommends testing after any significant change to your system. Pick up a radon test kit and run a short-term test to see where things stand. If levels are elevated, you can reduce your exposure by increasing ventilation in the lowest level of the home. Open windows, run a heat recovery ventilator if you have one, and limit time in the basement until the fan is back online.

Keep in mind that a radon fan not working does not always mean the motor is dead. I have seen cases where the fan was running but the manometer showed no pressure. The issue turned out to be a disconnected pipe in the crawlspace. The fan was venting into the crawlspace instead of outside, which is worse than having no fan at all. A thorough inspection by a qualified technician will catch these hidden failures.

Preventive Maintenance Matters

The best way to avoid being caught off guard by a radon fan not working is to check the system regularly. Look at the manometer once a month. If the reading changes, something is wrong. Listen for unusual noises. A fan that starts making a grinding sound likely has a bearing going bad. Replace it before it seizes completely. And keep the area around the fan clear of debris and moisture. A little attention goes a long way toward keeping your radon system reliable for years.

If you live in St. Louis and your fan has stopped, you are not alone. Air Sense Environmental sees this issue weekly. They can diagnose the problem quickly, whether it is a simple capacitor swap or a full fan replacement. The important thing is not to ignore it. A silent fan means radon is no longer being pulled from beneath your home, and that is a risk you do not want to take.