Radon System Not Working? Troubleshooting Guide

Your radon mitigation system has been running for months — maybe years — and something seems off. The manometer looks flat, the fan sounds different, or you just ran a test and the numbers are still high. Now what?

Signs Your Radon System Is Not Working

Before you panic, let's walk through the indicators. Some are obvious. Others require a test to confirm.

The Manometer Is Flat or Reversed

Most residential radon systems have a U-tube manometer — a small, liquid-filled gauge mounted on the PVC pipe, usually in the basement or utility area. When the system is working, the liquid levels are uneven, showing that the fan is creating suction. If both sides are level, the fan is not pulling air. If the liquid is tilted the wrong way, something is pushing air backward through the system.

Check this gauge regularly. It takes two seconds and tells you immediately whether suction is active.

The Fan Is Silent or Sounds Wrong

A working radon fan produces a low, steady hum. If you stand near the fan (usually in the attic or on an exterior wall) and hear nothing, the motor has likely failed. If you hear rattling, grinding, or intermittent buzzing, the bearings are going and failure is close.

Radon fans are designed to run 24/7. They do not cycle on and off. If yours is intermittent, something is wrong. For a breakdown of what different fan sounds mean, check out our guide to radon fan noise.

Post-Mitigation Test Results Are Still High

This is the definitive check. The EPA recommends re-testing within 30 days of system installation, and then every two years after that. If your follow-up test shows radon at or above 4.0 pCi/L, the system is not doing its job — even if the fan is running and the manometer shows suction.

A running system that does not reduce levels usually means the suction field is not reaching enough of the sub-slab area, or there are entry points the system cannot overcome.

Common Causes of System Failure

Fan Failure

Radon fans have a typical lifespan of 5 to 10 years, though some last longer and some fail sooner. They run continuously in environments that can include moisture, temperature swings, and condensation. Motor burnout is the most common failure mode.

Replacing a radon fan is a straightforward job for a qualified contractor. The fan itself costs $100 to $300 depending on the model, and labor adds another $100 to $250. Our radon fan comparison guide covers the most common replacement models and what to look for in a new unit.

Cracked or Shifted Slab

Concrete slabs crack over time. Foundation settling, soil movement, and freeze-thaw cycles all contribute. New cracks create new radon entry points that may be outside the suction field of the existing system. If your home has developed significant new cracks since the system was installed, the original design may no longer be sufficient.

Look for visible cracks in your basement floor, especially near walls, around floor drains, and at cold joints where different concrete pours meet. Hairline cracks are usually not an issue. Cracks wide enough to fit a coin edge are worth sealing and re-testing.

Missing or Degraded Seals

A properly installed system seals the suction point, the sump lid (if applicable), and major penetrations in the slab. Over time, caulk dries out, sump lid gaskets compress, and pipe boot seals deteriorate. Each gap reduces the system's ability to maintain negative pressure under the slab.

This is one of the easier fixes. Polyurethane caulk rated for concrete is inexpensive, and resealing accessible joints is something a handy homeowner can do. Just re-test afterward to confirm it made a difference.

Blocked or Damaged Discharge Pipe

The vent pipe that carries radon above the roofline can get blocked by ice, debris, bird nests, or physical damage from storms. A blocked discharge means the fan is trying to push air through a closed system — which kills airflow and can burn out the motor faster.

Visually inspect the pipe exit point on your roof or exterior wall at least once a year. In cold climates, ice blockage during winter is a known issue. Some systems include a condensation bypass or drain to reduce this risk.

Inadequate Original Design

Sometimes the system was undersized from the start. A single suction point may not create enough vacuum across a large slab or one with poor sub-slab communication (dense clay, for example). If the original installer cut corners — undersized pipe, wrong fan specification, insufficient sealing — the system may have never worked as well as it should have.

This is harder to fix because it often means adding suction points, upgrading the fan, or rerouting pipe. It requires a certified contractor to diagnose and redesign. For help with system maintenance best practices, our system maintenance guide covers what to check and when.

DIY Checks vs. When to Call a Pro

Here is a reasonable division of labor:

Safe to do yourself:

• Check the manometer reading weekly
• Listen to the fan for unusual sounds
• Visually inspect the discharge pipe for blockages
• Reseal small cracks and accessible joints with polyurethane caulk
• Run a short-term radon test kit ($15 to $40) to check current levels
• Replace a sump lid gasket if it has deteriorated

Call a certified contractor for:

• Fan replacement (involves electrical work and proper fan sizing)
• Adding suction points (requires core drilling and pipe routing)
• Diagnosing poor sub-slab communication (requires diagnostic testing)
• Any modification to the pipe routing or discharge location
• System redesign when the original install was inadequate

Typical Repair Costs

Straight up — most repairs are not expensive relative to a full system install:

• Fan replacement: $200 to $550 installed
• Resealing cracks and joints: $100 to $300 if done by a contractor (nearly free if DIY)
• Adding a suction point: $300 to $700
• Clearing a blocked discharge pipe: $100 to $200
• Full system redesign/replacement: $1,000 to $2,500+

Get at least two quotes before authorizing any work beyond a simple fan swap. And always insist on a post-repair radon test to confirm the fix actually worked.

When to Replace the Whole System

Replacement makes sense when the existing system has multiple failures, the original design was fundamentally flawed, or the home has undergone major renovation that changed the foundation or airflow dynamics. If you are spending more on incremental repairs than a new system would cost, it is time to start fresh.

A qualified contractor can evaluate whether targeted repairs will solve the problem or whether a redesign is the better investment. Find one through our mitigation contractor directory.