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Surging toilets

Q: The toilet in the bathroom on the second floor of our new home frequently surges, and the tank refills without being flushed. We’ve replaced the float mechanism twice already but still have the problem. Can you solve this mystery?

A: Peter Hemp, a plumber in Albany, California, and author of Plumbing a House, replies: I assume that by the word surge, you are indicating a running noise rather than a full-flush cycle. If this is the case, the problem is that water is slowly leaving the tank and flowing through the toilet bowl. When enough water has escaped, the float-activated fill valve allows more water into the tank (that’s the running noise you are hearing) until the valve shuts off again.

Unfortunately, replacing the float mechanism won’t cure this problem. Water is leaking from the tank because of a faulty flush-valve seal. All toilets have some sort of flush valve that keeps water in the tank between flushes. Depressing the handle on the toilet lifts the valve, allowing the water to enter the bowl and flush it clean. You can test the flush valve by adding a drop or two of dye or food coloring to the water in the tank after a flush. Let the toilet stand for a few hours. If the flush valve is bad, the water in the bowl should start to turn the same color as the water in the tank.

Once you’ve determined that the flush valve is in fact bad, shut the toilet-supply valve (under the tank) and flush the toilet. Remove the faulty flush valve and replace it with a valve made by the toilet manufacturer to ensure a perfect fit. Before you go to your plumbing-supply house, get the make and model number of your toilet, which should be cast into the back-inside wall of the tank.

From Fine Homebuilding 119, pp. 22 November 1, 1998