no hot water pressure

I have been out of town for a while and returned to find that I can not get hot water from my mohen shower mixing valve, hot water produces throughout all other sinks and shower faucets but the master shower it dribbles warm, and has full blast coldwater. I have opened all faucets together to blowout the line and still no results. Has anyone experienced this issue, and how can I go about resolving it. Please help need a hot shower..

Depending on the valve you have, there may be a balancing spool in the valve or one in the cartridge...they need to be removed and cleaned or replaced...I have always removed and cleaned them...vinegar works well along with some very fine wet or dry sand paper.. then a little silicone and it all slips back together...silicone only the valve and O rings...not the spool...

valve

Take the cartridge/stem out. Tap it on the floor a couple of times, or until you can shake it and feel/hear the spool sliding back and forth, then reinstall it. Make sure you reinstall it the same way it came out or your hot and cold sides will be reversed.