Most radon systems use the same design: a pipe through the basement slab or crawlspace, a fan that pulls soil gas from under the house, and a vent above the roof. When something goes wrong, it is usually one of a few problems you can check in a few minutes.
Reading the manometer
The U-shaped tube of colored liquid on the pipe is a manometer. It shows whether the fan is pulling a vacuum under the slab.
- Liquid levels uneven: the fan is pulling suction. Good.
- Liquid levels even: no suction. The fan is off, failed, or unplugged, or the pipe is blocked. Check the breaker and the fan first.
- Reading drifts a little with the weather: normal. Note the level your installer marked; a large, lasting change from that mark is worth a call.
A working gauge shows suction, not radon. Only a test tells you the level in the house.
Still high after mitigation
- Retest properly with the house closed, for at least 48 hours, on the lowest lived-in level. A short test after a big weather change can mislead.
- Call the installer. Many guarantee a result below 4 pCi/L and will adjust the system at no charge.
- Seal the leaks. An open sump pit, floor drains, cracks and gaps around pipes let soil gas bypass the suction. An airtight sump lid is one of the most common fixes.
- Add suction. Slabs with poor gravel underneath, or homes with a slab plus a crawlspace, may need a second suction point or a crawlspace membrane connected to the system.
- Upsize the fan if the suction is weak across a large slab. Your installer can measure this.
Fan noise
- Humming carried through the house: vibration through the pipe and framing. Rubber couplings and isolating the mounts usually fix it.
- Gurgling or dripping: condensation running back down the pipe. Normal in small amounts; the pipe should slope so water drains to the soil.
- Grinding, rattling or a rising whine: bearings wearing out. Plan to replace the fan.
- Exterior pipe in cold climates: ice at the outlet can choke the vent. Check after cold snaps.
Replacing a fan
Radon fans run around the clock, so they wear out eventually; warranties commonly run about five years. Replace like with like unless your installer recommends a different size, and check the manometer and retest afterward. The fan must be outside the living space (attic, garage or exterior) and the vent must end above the roof edge, away from windows and doors.
Keep an eye on it
A continuous radon monitor shows levels day to day, so you notice a failed fan in a week instead of at the next test. See radon testing at home for which monitor to use.