What to Do When Your Radon Fan Is Not Working

Living in St. Louis, I have seen plenty of basements with radon systems that were installed years ago and then forgotten. The fan runs quietly in the background, pulling soil gas from under the slab and venting it above the roofline. When that fan stops, the whole system goes silent. And because radon is invisible and odorless, you might not notice the problem until a radon test kit shows elevated levels. If your radon fan is not working, the first step is to figure out why, and the second step is to decide whether it can be repaired or needs replacement.

Start With the Obvious: Power and Connections

Before you assume the fan motor is dead, check the basics. Look at the circuit breaker that feeds the fan circuit. In older St. Louis homes, I have found breakers that were tripped by a power surge or by a separate appliance on the same circuit. Reset the breaker and see if the fan starts. If it does not, move to the disconnect switch. Some systems have a local disconnect near the fan, often in the attic or crawlspace. Make sure it is in the on position. Also check the fan controller if your system has one. Some controllers have a low-speed setting that barely moves air, and it can look like a failure.

Listen and Look for Fan Operation

A working sub-slab depressurization fan makes a distinct hum and moves air through the PVC piping. If you hold a piece of tissue paper near the vent pipe termination outside, it should pull the paper toward the pipe. If there is no suction, the fan is not running. A manometer can confirm this. Many systems have a manometer installed on the pipe to show static pressure. If the fluid levels are equal, you have no pressure difference and the fan is stopped. A pitot tube can also be used to check airflow, but for most homeowners the manometer is the easiest indicator.

Common Causes of a Non-Working Fan

Over the years, I have seen three main reasons why a radon fan not working turns into a service call. The first is a failed capacitor. Many fans use a capacitor to start the motor. When that capacitor weakens or fails, the fan may hum but not spin, or it may not start at all. Replacing a capacitor is a simple fix for a technician, but not something most homeowners should attempt because the wiring inside the fan housing can be tricky.

The second common cause is a problem with the fan leads. These are the electrical wires that connect the fan to the power source. In crawlspaces and attics, rodents sometimes chew through the insulation, or the wires can become corroded if moisture gets into the junction box. A break in the fan leads will stop the fan completely. A technician can splice or replace the damaged section.

The third cause is mechanical wear. Fans like the RadonAway GP-201 or the RN101 are designed to run continuously for years, but bearings do wear out. If the fan sounds rough or rattles when it does spin, the motor bearings are likely shot. At that point, replacing the fan is usually more cost-effective than rebuilding it.

Check for Blockages in the System

Sometimes the radon fan itself is fine, but the system cannot move air because of a blockage. In a sub-slab depressurization system, the PVC piping runs from the fan to the soil under the slab. If the pipe is crushed, filled with water, or blocked by debris, the fan will struggle or appear to be not working. A blocked pipe can make the fan run but with no effective airflow. A technician can test the system pressure and use a manometer to see if the fan is fighting a restriction. If the pressure reading is higher than normal, there is a blockage somewhere. If the reading is zero, the fan may be dead or the fan leads may be broken.

When to Call a Professional

If you have checked the circuit breaker, the disconnect switch, and the fan controller, and your radon fan not working still is not running, it is time to call a professional. In St. Louis, companies like Air Sense Environmental specialize in radon system repair and fan replacement. They carry common replacement fans such as the RadonAway GP-201 and the RN101, and they know the local soil gas conditions. A technician can diagnose the problem quickly, test the capacitor, check the fan leads, and verify the system pressure with a manometer. They can also inspect the PVC piping for damage and test the Radon Seal around the pipe penetrations to make sure the system is airtight.

Consider Upgrading to a Heat Recovery Ventilator

If your fan has failed and your home has a tight envelope, you might think about adding a heat recovery ventilator as part of the system. A heat recovery ventilator exchanges stale indoor air with fresh outdoor air while recovering heat. It is not a direct replacement for a radon fan, but it can work alongside a sub-slab depressurization system to improve overall indoor air quality. Some newer radon fans are designed to be more energy-efficient and quieter than older models. The RadonAway GP-201, for example, has a reputation for reliable laminar flow and low power consumption.

Testing After Repair or Replacement

Once the radon fan is repaired or replaced, you should test the system to make sure it is working properly. Use a radon test kit to measure the radon level in the lowest lived-in level of the home. The EPA recommends taking action if radon levels are at or above 4 picocuries per liter. A properly functioning sub-slab depressurization system should bring levels well below that. Run the fan for at least 24 hours before starting the test, and follow the test kit instructions carefully.

Preventive Maintenance

To avoid a repeat failure, inspect your radon system once a year. Look at the fan leads for signs of wear or rodent damage. Check the PVC piping for cracks or loose joints. Make sure the Radon Seal around the pipe is still intact. Listen to the fan for any unusual noise. If you have a manometer, note the normal pressure reading so you can spot a change later. A small investment in annual inspection can save you the cost of an emergency service call.

Final Thoughts

A radon fan that stops working is not a crisis, but it is a problem that should be addressed quickly. The longer the fan is off, the more soil gas can enter the home. In St. Louis, where the geology produces significant radon potential, a non-working fan can lead to elevated test results. If your radon fan is not working, start with the simple checks and then call a professional if needed. With the right diagnosis, most fan failures are easy to fix. And once the fan is running again, you can return to peace of mind knowing your family is breathing cleaner air.