The flapper valve in the toilet in my apartment was recently replaced, since it had a small leak. The new one has a perfectly good seal, but sometimes just gets stuck open. It looks like it's just gripping a bit too tightly on the hinge - when it tries to close, it moves partway down and just hangs there, and a little jiggle of the lever is enough to make it drop. What should I do about it?
If you purchased one of the generic replacements, they usually come with both the slide on and hinge mounting rubber parts attached. If your mounting is the two side pin type, then you must cut the connecting tabs of rubber that hold the slide on rubber ring, and discard it. If you slide the flapper on with the ring and also use the side hinges, it will not work properly. You can only use one mount type.. slide on or side hinge. Hope this is your situation, easy fix.
I ended up just pulling the valve off and sanding inside the snap-on hinge bits. It didn't take much to get it moving smoothly - they didn't seem very rough before I sanded, and I didn't widen them very much.
Add weight to the flapper: find a half-inch nut, remove the chain from the lever, put the chain up through the nut and re-attach it to the lever. The chain will keep the nut from getting in the way of closure.
The flapper didn't close completely or just hang open due to the lack of weight if momentum is the factor. I added some necklace chain or coin to help while the flapper dropped.