The water in the shower does not get very hot. I thought it might be the diverter valve on the knob of the shower, so I bought a new shower head kit. When trying to install it I noticed that when the main hot water valve to the shower is on there is no hot water coming into the shower; there only appears to be cold water coming to the shower. Is this a bad shower valve or is this the prevention from scalding on the shower fixture, or is this something with the hot water pipe?

Sounds like it may be an integral stop not open on the hot side. Are you saying you have no flow from the hot side?

What's the brand name of your shower valve? Does it have a temp control,((Posi-Temp) in the valve? Tom