The toilet fill valve (sometimes known generically as a ballcock) is relatively easy to repair if you happen to have a Fluidmaster brand valve. Often, repairing a fill valve is done by simply replacing the entire fill valve, but Fluidmaster fill valves can be repaired by just replacing a seal inside the unit. If your Fluidmaster fill valve is not shutting off all the way or not filling quickly like it did when it was new, then replacing or cleaning the seal will most likely fix the problem.
The replacement seals for a Fluidmaster fill valve are widely available at home centers and hardware stores. You should have no trouble finding one. And while you're at it, pick up an extra to have on hand the next time you have a problem. They are very inexpensive.
To Replace the Seal in a Fluidmaster Fill Valve:
- Shut off the water to the toilet. To get access to the seal, you will have to take apart the fill valve, and for that, the water needs to be off. Usually, you can do this simply by shutting off the water supply shutoff valve below the toilet
- Hold the fill valve shaft and push the float cup up towards the top of the fill valve. While holding the shaft body with one hand, use the other hand to turn the cap on top of the fill valve counterclockwise 1/8 of a turn. Pushing down on the cap while turning can help it turn easier. The top should pop off and you can then get to the seal inside.
- Replace the seal. Just lift out the old seal and make sure that the inside of the Fluidmaster fill valve is clean before putting the new seal in place. Then just insert the little hole in the seal onto the needle-like stem and push it flat all the way around.
- Put the fill valve back together. A 1/8 clockwise turn while holding the body of the fill valve will lock the unit back together. Then, turn the water back on and check to make sure that the new seal fixed the problem.
Note: Sometimes that seal can get clogged up with sediment or sand, and the solution may to simply take apart the valve and clean away any sediment from around the seal.