No hot water pressure in the shower

The hot water just trickles out of the shower head.

I shut the water to the house off and removed the stem. Still only a trickle when I turned the water back on. However, when I turn the hot water on in the bathroom sink and then the cold water, water flows freely from where the stem was pulled and from the shower head when I put the stem back in.

Any ideas?

Thanks!

 

Sounds like a typical problem with MOEN shower faucets. If you need to pull out to the handle to turn the water on and then turn it for temp control, it's a MOEN. Inside the cartridge there is a part that when shaking the cartridge in your hand you hear and fell the rattle. this somehow gets stuck. Remove the cartridge and tap it on the ground a few times and you'll hear. You can put it back in or get a replacement. There are all kind of hints on this site on how to remove the cartridge and it can be very difficult to do.

Here is an entry that I did after replacing a MOEN POSI TEMP cartridge with a DANCO brand replacement. I had help both my friend and their daughter (two homes) with the same problem as you have. https://terrylove.com/forums/showthread.php?32514-Water-Hammer-knock-DANCO&highlight=

 

I have a problem with an American Standard R120 shower valve (the type where the lever moves up/down for volume, and left/right for temperature). Sometimes no hot water comes out. If the lever is all the way on the hot side, no water comes out at all. If I turn it back and forth, eventually there's a thump, and then the hot water flows.

Nothing looks wrong with the valve. Is there anything I can try, short of replacing it?