Locating a leak and repairing a running Mansfield toilet

Repairing a leaking or running Mansfield toilet

Typically there are two causes of a leak that causes a Mansfield toilet to run:

  1. The water level is set too high
  2. The flush valve seal is damaged

However when I was trying to stop my running toilet I found out that the culprit was neither of these. After hours of pulling my hair out and searching the internet I found that my problem wasn’t one that was listed elsewhere; I’ll get to that below.

Before we know what parts need to be fixed or adjusted, we need to figure out where the problem lies.

Stopping a leak or running toilet by adjusting the water level

Does the toilet only leak or run after it has been flushed? If so it may be that the water level is in fact too high and the running is caused by excess water overflowing and going down the overflow tube which ends up in the bowl (hence causing the running sound).

To fix this problem note where the water fills up to in the tank after a flush. Is it above the Water Level line? Is it in fact overflowing and going down the overflow tube? If so, grab a phillips (+) screw driver and tighten the screw at the opposite end of the float ball to lower the water level.

It may take a few test flushes to get the level right, but a good trick is to tighten it a few extra turns (be sure not to make it too tight). The more you tighten it, the lower the water level is. Once the tank refills and it is still below the water line, you can slowly start loosening the screw which will raise the water level. This method will allow you raise the water level without having to guess where it should be.

Changing a damaged valve seal

The next most common cause of a leaky or running Mansfield toilet is a damaged valve seal. If your toilet is still running and needs repairs after the above step, then you will likely have to disassemble the flush valve float. Check out A walkthrough for disassembling a Mansfield toilet for basic repair for instructions on how to do this.

Before you do this be sure to shut the water off to the toilet, otherwise things will get wet quick. The water shut off is generally located below the toilet on the left side. To turn it off turn the valve all the way to the right. Once you have the water shut off flush the toilet again to empty the tank.

Once you get the flush valve float taken apart you should be able to see a red seal at the bottom of the tank. This seal is supposed to stop leaks from the tank into the bowl hence when it is damaged it can be the culprit behind a running toilet.

To replace the valve, pull the old seal off. It might be a tad brittle if it is older, but if you are replacing it you shouldn’t have to worry about damaging it. If it doesn’t seem to be coming off, you may need to give it a good pull or try to stretch it out of its groove.

Replacing the seal isn’t difficult, but it is crucial that you put the seal back in the correct spot. There are actually two grooves at the bottom where the seal is and it is important to get the seal in the top groove. This might take a couple of tries, however it isn’t hard.

If you aren’t sure what groove you are in you can use your fingernail (or a butter knife if you don’t have long fingernails) to feel around to see if there is another groove above where your seal is. If you are having trouble getting the seal in place (particularly in the part closest to the tank) then you can get the seal into the proper groove and then slowly pull it to the left or right. If it is in the groove then it should slide along in the groove and allow you to use the same accessible spot to another length into the groove.

Once you get that seal replaced then the toilet should stop running, if that was in fact the problem.

A damaged float valve

When I was trying to fix my Mansfield toilet I tried both of the steps above many times and I still couldn’t stop it from running. After racking my brains out and checking dozens of different sites on the internet, I found out what the problem was: the flush valve float had a small hole in it.

Whilst replacing the flush valve seal for the third time or so, I decided to give the flush valve a good wipe down in case there was any debris on there that I couldn’t see. While wiping it down I happened to notice a small crack and a small hole in the plastic.

I ended up having to run around to a few shops (apparently Mansfield toilet parts aren’t readily stocked everywhere) and I eventually found a complete flush valve float replacement. All I needed was the actual flush valve float, so I slid the new one on (along with a new seal since I had one) and that fixed the problem.

Be sure to visually inspect all the parts that you can if the above steps do not work as all it takes is a pin size hole to cause a running toilet.

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