This thread was VERY helpful! I was about to tear the entire toilet apart to replace the flush valve. I purchased a new flush valve for $7.50 from Lowes which came with directions on how to replace the entire thing. Fortunately, I came across thread and ended up spending 5 minutes to replace a washer. Thanks!
its the seal in the bottom of the tank. The seals are defective. They loose their shape and get displaced into the opening that releases the water into the bowl causing the plunger to get stuck. Call Mansfield and ask for a replacement seal. They should furnish you a free one.
Thanks for the phone number. Have the same prob w/ my mansfields. Called the number. Can't believe they're sending them out for free. Sweet.
Meanwhile I figured out a temp and immediate fix. I lifted the plunger contraption and unseated the red o ring seal and kinda worked it in my hands a bit and re-seated it. Much easier to flush now - until I get around to replacing it. Make sure you seat it exactly or you'll get a running toilet.
You may recall that I called Mansfield and they sent me two seals for free. I have two Mansfield toilets in my house. I did the seal replacement in one and it worked fine, and still does. But in the other toilet, the seal never quite did its job and the toilet would run from time to time. The directions said something about using Vaseline (I think) to help the seal, but ultimately I just decided to replace the whole Mansfield valve with a new complete flapper-type valve system. This has worked fine. When the other toilet needs a new seal, I will use the free replacement seal again, but if I run into the running toilet problem again, will just do the complete replacement. As I said, one out of two ain't bad but I believe the flapper valve is a much better system than Mansfield's.
You can also flip the current seal you have over as a temp fix, until you get back from the hardware store, or until Mansfield mails you your new seal. I also found a good "how to" video at www.griggindustries.com; just go to the Mansfield section and click on the flush valve seal and there is a how to video. After watching the video, the whole process took me less than 5 minutes to complete!
So it only took two days to receive the free handle set and seals (they sent two).
My seal was actually flaking apart, but I was able to easily remove the assembly (remove tubing from refill tube) then turn the quarter-sized disc top of the tube assembly and it lifts off. Then you just pull off the old one and put the new one on (make sure it sits in that same ledge). It flushes like a feather now!
A+ for their customer service. It took about 5 minutes to replace the seal as well as replace the handle assembly, and I am a "not that handy (but willing to try)" girl!