Leaking Toilet

Ever hear a hissing noise from your toilet? It can be very annoying especially late at night. It can be a steady hissing or an intermittent hiss that occurs at a regular frequency. Here's what is happening.

The standard tank type toilet is a rather simple device. Understanding how it works will help you understand what can go wrong.

The tank at the back of the toilet is a reservoir that holds all the water needed for a flush. It is filled to a set level and contains around three gallons of water. Newer toilets hold a lot less for water economy. The water leaves the bottom of the tank when the flush lever is operated. Twisting the flush handle pulls a flapper valve from the bottom of the tank so that water can rush into the bowl and flush away the waste. When the water level in the tank drops a float ball, mounted on a long rod, falls with the water level until the tank is emptied. Newer toilets use a similar device which uses a float mechanism that slides up and down on a post mounted to the bottom of the tank.

As the float assembly drops it activates a valve which permits water to enter the tank. At the same time the flapper valve which opened during the flush cycle now closes by gravity puling it back into place over the opening in the bottom of the tank. Water now enters the tank to refill it. At the same time a small tube attached to the filer valve opening diverts a small amount of water into the overflow tube in the tank. That overflow tube is there to prevent the tank from overfilling if there were a fault in the filler valve. It is connected directly to the bowl side of the flapper valve hole and dumps water back into the bowl. The small tube mentioned above is there to ensure that the toilet bowl is filled completely with water during the tank refilling cycle. If it is removed the bowl may not fill completely with water.

Here is a picture of what I have just described:

So, now that we understand the mechanics of the system, what can go wrong to cause that annoying hissing that keeps you awake at night?? It is the fill valve that is hissing. There is either a leak in the flapper valve or a faulty or misadjusted fill valve. How do you tell which is the problem?

After the toilet has been inactive for about an hour remove the tank cover and observe the water level in the tank. If it is too full then water will be spilling into the overflow tube. The cause of this problem is usually a faulty filler valve. To find out just flush the toilet and watch the filling procedure. The tank will fill to a preset level rather rapidly. At that point the float mechanism should turn the water off completely. If it is leaking then the level will slowly rise until the water dumps into the overflow tube. If this happens you need to replace the filler valve.

If on the other hand you observe that the water is well below the overflow tube yet there is still a hissing noise then the problem is most likely a leaking flapper valve. To find out you can reach behind the toilet and turn off the water supply. Wait a few hours and look at the water level again. If water is leaking into the toilet bowl then the tank will have emptied either partially or completely depending on how bad the flapper is leaking. If this is the case then replace the flapper valve.

One final note. If the small tube that goes from the fill valve to the overflow tube is too long and sticks down too far into the overflow tube it is possible with some valves to have water siphon into the overflow tube and cause the level to drop sufficiently to cause the tank fill valve to turn on to refill the tank. Just make sure that the makeup tube is not stuck more that a quarter of an inch into the overflow tube and you will eliminate this as a possible problem.

There are several companies that sell a complete unit to replace both the flapper valve and the fill valve. Most home repair supermarkets and hardware stores sell these assemblies for under ten dollars, a small investment to end that annoying hissing noise and save water at the same time.

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