A high radon reading after mitigation usually means something simple and fixable, not a total system failure: a fan that lost power, a disconnected pipe, or a test run under the wrong conditions. Start by confirming the fan is running and the warning device shows normal pressure, then retest under closed-house conditions. If both check out and levels are still high, treat it as a real system problem and call a professional.
TL;DR:
- Keep windows and exterior doors shut for at least 12 hours before and during testing; use a continuous monitor for 48 to 72 hours.
- When a verified, working system leaves readings above 2.0 pCi/L, ask a contractor to test whether suction reaches the full slab.
- Call a qualified mitigation professional if a properly conducted retest averages 4.0 pCi/L or higher, or if fan operation cannot be confirmed.
- Request written verification testing after repairs, and keep readings, gauge photos, and a timeline for future maintenance or a home sale.
Table of Contents
- Priority troubleshooting checklist: 8 quick checks you can run now
- Common causes a mitigation system stops reducing radon
- How professionals verify system performance
- Step-by-step homeowner checks to run before calling anyone
- When to call a qualified mitigation professional
- Why verification and documentation matter more than the install itself
- How Cincinnati Radon Solutions can help with repair and verification
- FAQ
- Sources
Priority troubleshooting checklist: 8 quick checks you can run now
Before assuming the worst, work through these checks in order. Most failed-looking systems turn out to have one of these simple, fixable causes.
- Confirm the test was valid. Closed-house conditions mean windows and exterior doors stay shut except for normal entry and exit, for at least 12 hours before and during a short-term test.
- Check the device type and exposure time. A charcoal canister or continuous monitor placed near a drafty window, in a high-traffic area, or for too short a period will skew results.
- Check fan power. Walk out to the fan (usually in the attic, garage, or exterior wall) and listen or feel for vibration. Check the breaker it's wired to, and note whether it's on a switched circuit someone could have shut off.
- Read the manometer or warning device. This small gauge or alarm, required under the EPA's Consumer's Guide to Radon Reduction, shows whether the fan is creating suction. Photograph the reading with a timestamp.
- Inspect visible piping and the roof discharge point. Look for disconnected joints, crushed sections in a crawlspace or attic, or a cap blocking the outlet.
- Check sump pits and floor drains. Standing water or an unsealed sump lid can short-circuit the suction the system relies on.
- Look for short-circuit airflow paths. An open garage door connected to living space, an oversized return duct near the slab, or unsealed utility penetrations can all pull conditioned air instead of soil gas.
- Note recent changes to the house. New HVAC equipment, window replacements, an addition, or a renovation can alter indoor pressure enough to change radon behavior without any mitigation failure at all.
Write down what you find for each item, even if everything looks fine. A simple log of dates, readings, and observations becomes valuable later if you need a professional opinion.
Pro Tip: Photograph the manometer gauge every time you check it, not just once. A single reading tells you little; a pattern over a few days tells you whether the fan has been running continuously.
Common causes a mitigation system stops reducing radon
Each of the checklist items above points to a specific mechanical reason levels can climb back up. Understanding the "why" helps you describe the problem accurately if you call a contractor.
- Fan failure or a switched-off circuit stops suction immediately. Radon can return to pre-mitigation levels within hours once the fan stops moving air from beneath the slab.
- Short-circuiting of the suction field happens when the system pulls conditioned house air instead of soil gas, often through an open garage connection, a poorly sealed sump lid, or ductwork buried near the collection point.
- Insufficient pressure-field extension means the vacuum created under the slab doesn't reach far enough to cover the whole foundation footprint, usually because the soil is dense clay or because the original design used too few suction points for the house's size.
- Water-related failures occur when a flooded sump pit, a rising water table, or an untrapped floor drain blocks the air pathway the system depends on.
- Installer issues include missed communication paths between slab sections, gaps in sealing around the suction pipe, or exhaust routed too close to a window or door where it can re-enter the house.
- Seasonal and stack-effect variations can shift radon readings up or down by a measurable amount between winter and summer without any actual system failure, since indoor-outdoor pressure differences change with temperature.
Most of these causes trace back to installer errors, communication gaps, water issues, or interference with fan wiring, and most respond well to added suction points or a fan upgrade rather than a full system replacement.
How professionals verify system performance
When homeowner checks don't explain the problem, a mitigation contractor has several diagnostic tools that go beyond a visual inspection. These are worth asking about by name.
- Manometer and flow measurements establish a baseline reading at installation, then compare it against current readings to see whether suction has dropped.
- Pressure-field extension testing involves drilling small monitoring holes at points away from the suction pipe to confirm the vacuum reaches the whole slab, not just the area closest to the pipe.
- Smoke-stick diagnostics release a visible stream of smoke near suspected leak points, cracks, or sump lids to show whether air is being drawn in correctly or escaping where it shouldn't.
- Grab-sample measurements taken inside the vent pipe and at individual suction points help a contractor find "hot spots" where radon concentration is unusually high, pointing to a specific trouble area.
The EPA's guidance on confirming system performance lists exactly this combination of checks: visual inspection, pressure and flow measurement, pressure-field extension, and smoke testing.
A properly functioning system should bring indoor levels to 2.0 pCi/L or lower in most homes, well under the EPA action threshold. A reading that stays above that range after a verified, properly running system suggests a genuine design or installation gap rather than normal variation.
Step-by-step homeowner checks to run before calling anyone
This sequence turns the checklist into a short session you can complete in under an hour, with results worth sharing with a contractor if the problem persists.
- Confirm the fan is powered. Check the breaker and look for any switch in the circuit. Do not open electrical junction boxes yourself: if the wiring looks damaged or you're unsure, call a licensed electrician instead of troubleshooting it directly.
- Read and photograph the manometer or warning device. Log the reading with a timestamp, and repeat this once or twice over the next day to confirm it's stable.
- Walk the piping route from the basement or crawlspace to the roof. Check joints, clamps, and the flashing where the pipe exits the roof for cracks or separation.
- Inspect the sump pit, floor drains, and any buried ductwork nearby for standing water, debris, or an unsealed lid that could be pulling air from the wrong place.
- Restore closed-house conditions and either run a new short-term test or place a continuous monitor for 48 to 72 hours to see whether the reading stabilizes.
- Prepare a one-page summary. Include your photos, logged readings, and a short timeline of when you noticed the problem and what you checked.
Pro Tip: Keep the closed-house conditions consistent with the original test, since comparing a retest done with windows open against an initial test done with windows closed will give you a false sense of either improvement or failure.
When to call a qualified mitigation professional
Call a professional when a properly conducted retest still averages 4.0 pCi/L or higher, or when you can't confirm the fan and warning device are both working. A professional visit typically includes:
- A full visual inspection of piping, fan, and exterior discharge point.
- Manometer and flow measurements to confirm suction strength.
- Pressure-field extension testing at multiple points under the slab.
- Smoke testing at suspected leak points and a check of sump pits and nearby ductwork.
Common fixes include adding suction points, replacing or upgrading the fan, sealing communication paths across the slab, relocating the exhaust point, or addressing a water issue in the sump. Ask for written post-repair verification testing, since an objective follow-up test matters for your own peace of mind and for any real-estate disclosure down the line. If you're selling, buyers and their agents often expect documentation like this; a clear guide to why buyers request repairs explains how inspection findings typically shape negotiations.
Why verification and documentation matter more than the install itself
A mitigation system is only as good as its last verified reading. Every foundation behaves differently, which is why a design that works well in one house can underperform in another with different soil or slab conditions. Post-install verification testing exists precisely to catch that gap before anyone assumes the job is finished.
Documented testing also protects you later, whether that means planning fan maintenance on a predictable schedule or having a clean report ready if you sell the house. A reading on paper, tied to a date and a working system, is worth more than a one-time assumption that everything is fine.
— Yoshua
How Cincinnati Radon Solutions can help with repair and verification
When a system stops performing, we design our fixes around what's actually happening in your foundation rather than a generic replacement. Our radon system repair and fan replacement service addresses the most common failure points: dead fans, disconnected piping, and sealing gaps, and we follow every repair with verification testing to confirm the fix actually brought levels down.
- Custom-designed systems based on your specific foundation type, not a one-size layout.
- Certified installations with documentation suitable for real estate transactions.
- Fixed written quotes with no added costs after quoting.
- Post-installation verification testing included with every mitigation project.
If your readings are still high after an existing system was installed, or if you just want an independent check on a system someone else installed, you can review our full services list or get a sense of typical repair and mitigation costs before scheduling a visit.
This article is general information, not a substitute for advice from a qualified doctor. Consult a qualified healthcare professional about your own circumstances before acting on anything here.
FAQ
Does radon mitigation work well?
Properly designed and verified systems are highly effective, often reducing indoor radon to 2.0 pCi/L or lower. Performance depends on site-specific design and ongoing fan operation, which is why post-install verification testing matters.
Does radon go up at night?
Radon levels can shift with daily temperature and pressure changes, and many homes see somewhat higher readings overnight when windows and doors stay closed and indoor-outdoor pressure differences are greatest. This is a normal pattern tied to house conditions, not necessarily a sign of system failure.
How do you install a radon fan in an attic?
Attic fan installation involves routing the vent pipe from the suction point below the slab up through the house to a point above the roofline, with the fan placed in the attic section of that pipe for easier access and quieter operation. This work involves electrical connections and roof penetrations best handled by a certified mitigation professional rather than as a homeowner project.
Can you sell a house with high radon levels?
Yes, homes with elevated radon can be sold, but many buyers and their agents request testing, mitigation, or a price adjustment once levels are disclosed. Having documented testing and mitigation records on hand typically makes the transaction smoother for both sides.