intermittent toilet running

[boblc123]

Hi all

I just replaced the fill valve in my toilet with a Fluidmaster 400a. Everything seemed fine at first. The tank would fill to about a half inch below the overflow tube and then stop. However, after a period of a few hours, I came back into the bathroom only to find the toilet running. I removed the tank lid and could see that the tank was overfilling and allowing water to flow into the overflow tube.

I flushed the toilet, water then filled the tank to a half inch below the overflow tube and stopped. A few hours later, the toilet was running again and water was going into the overflow tube. What could be causing this? Why is the valve shutting off at the proper time, then engaging later and never turning off?

 

[Jeff Handy]

Make sure the length of the bowl refill rubber tube is not too long, not hanging down too low into the overflow pipe.

If too long, it can cause a siphon effect that drains water from the tank.

There should be a little plastic gizmo that clips onto the overflow and accepts the bowl refill tube, to direct water down the overflow.

Also, make sure you adjust the height of the fill valve to be well above the “critical level”, read the instructions, so that the air gap is above the tank water level.

 

[Rickyman]

You should’ve flushed the supply line. Now you have to take off the top of the fill valve and flush out the debris

 

[boblc123]

Make sure the length of the bowl refill rubber tube is not too long, not hanging down too low into the overflow pipe.

If too long, it can cause a siphon effect that drains water from the tank.

There should be a little plastic gizmo that clips onto the overflow and accepts the bowl refill tube, to direct water down the overflow.

Also, make sure you adjust the height of the fill valve to be well above the “critical level”, read the instructions, so that the air gap is above the tank water level.

my overflow tube has a little round circle on top that you slide the hose into. I didn’t use the clip provided with the valve. Perhaps I will try using the clip. Can you explain the siphon effect? How does it siphon water out of the tank if it’s in the overflow tube and there is no water in the overflow tube. Where would it suck water from?

 

[Jeff Handy]

If the bowl refill hose is too long, then the weight of the water hanging way down in the overflow tube can actually pull more water behind it, from the tank.
This is a siphon.
Water being lifted uphill then dropped downhill.

As long as the level of water in the tank is higher than the level at which the water is exiting the end of the tube, the water is essentially just falling downhill.
And the fill valve will run, so the tank water level will never drop enough to stop the siphon effect.

Using the clip keeps the exit point of the water up high enough to defeat that effect.

However, as Rickyman suggested, the fill valve might also be clogged with minerals or crud, so it can’t properly shut off.

When you open and close a rarely used shut off valve, trapped minerals can be released that end up in the tiny orifice of the fill valve.
You can take apart the top of the valve, there is a little plunger that gets clogged up.

You can find many videos on Youtube showing how to open and clean the fill valve.

You can also get a little rebuild kit if needed, so you don’t have to take out the entire fill valve.

 

[Jeff Handy]