Hey there. I purchased a Grohe 34126 thermostatic valve in 2006. Installed in 2009. Been just fantastic all this time, but recently I am unable to get really hot water, the kind that makes you want to stay in the shower. I can get hot hot elsewhere in the house, but not the shower or tub. It hits a certain moderate temperature and will not increase. A lot of the info I find out there is for new installs, but mine was working just fine and only recently has been a problem. Any ideas? Thanks.