Help with Moen Monticello single handle

I am in desperate need of info about my Moen Monticello single handled bathtub Posi-temp water control/shower control. It just gets hot enough to take a shower on SOME occasions,not every time, whats with this stupid thing,my house is 2years old and we had a BAD plummer install the faucet.
I can't find out anything from the computer,luckily I found this forum,any ideas what is wrong with this crazy thing?

faucet

IF the water in the system is hot enough, then you may just have to adjust the temperature limiting stop in the handle. The installing plumber would not have been able to do it if the water heater was not working when he finished installing the faucet.