I have a float-cup fill valve, Fluidmaster 400 model series. The classic solution to adjusting the water level is to turn the screw in a clockwise manner to make it go lower and counterclockwise to go higher (unless if I have reversed that).

Well, turning this screw in either direction seems to have little impact on the final water level which is above the water line. Actually if I go all the way high there is a possibility that the toilet won't stop running but I can't get the water to be anywhere near the water line on the lower end, it is always going to be above it by a bit.

So if I manually hold the, and I hope I have this term right, cylindrical plastic float in the up position the water will cut off and that is a way I can get the water to stop before it hits the water line. However, if I do not touch this cylindrical plastic float, it has trouble raising to the proper level and that is why it is late to shut off the water because the cylindrical plastic float on its own can not reach the proper height. On top of that, it looks like the cylindrical plastic float might even slip down a little bit so it has trouble maintaining its current height.

What could be causing issues with the ascension of the cylindrical plastic float and making the screw of little use to adjust the final water level?

1 Answer 1


Your toilet tank fill valve may need replacement if it is not adjustable in the way that I will describe. On valves that are adjustable the overall height of the valve / float assembly may need to be adjusted downward to lower the whole top of the unit. This will lower the overall range that the float works within.

If you need a replacement get something like shown here:

enter image description here

Picture Source

These units are available at home centers and hardware stores and are not that expensive. (Probably about the cost of two lattes at the coffee shop).

Note the portion of the base that is dark gray in color and the upper part that is the much lighter color. That lower part adjusts by screwing in or out of the upper part. This sets the position of the valve / float in the tank. The screw assembly is really just allowing a fine tuning of the water level. Generally the height adjustment is made when installing the unit.

  • Thanks I will take a look to see if I can adjust the overall height. When taking off the fill cap, there looks like there is a small piece of plastic broken. I don't know if this would affect the overall performance of the fill valve, but if it does and I cannot adjust the overall height I will have to get a new fill valve.
    – demongolem
    Jun 20, 2020 at 20:01
  • Actually, even though I ripped up my one finger pretty good, I was able to adjust the overall height of the unit (that is I was able to lower it). It seems that the overall water level has decreased a satisfactory amount such that it will stop and it likely not into a cycle of dropping and filling every few hours. Thanks.
    – demongolem
    Jun 20, 2020 at 20:19
  • @demongolem - Very often if your toilet tank valve is cycling in a fill followed by a level decrease over time it is due to a leaking flapper valve in the bottom of the toilet. Those need replacement more often than the filler valve, especially if there is chlorine additive in your water supply.
    – Michael Karas
    Jun 20, 2020 at 21:47

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