Look at the gauge or monitor on the pipe. Ohio requires every active system to have one, and a manometer must be marked with its reading at start-up. If the liquid has leveled out or the alarm is on, the fan is not pulling. Retest every two years.
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A U-tube manometer shows suction as a difference in liquid height between its two sides. Compare today's reading with the start-up mark; a large drift either way deserves a call, and level liquid means no suction at all. Electronic monitors have to be wired to circuits that are not switched and must reset on their own after a power outage. Check the obvious as well: the fan in the attic or on the outside wall should be running, and the breaker labeled RADON REDUCTION SYSTEM should be on. A healthy gauge proves the fan is moving air; it does not prove the air you breathe is below 4 pCi/L. That is why Ohio installers must advise retesting at least every two years and after major changes. Our repair service covers fans, gauges, and seals.