*PLUMBERSSTOCK EXPERT* responded:
There can be many explanations for that anomaly, however the most likely in regards to this valve is that there is something blocking the flow through the cartridge. I have heard that there is a way to put this cartridge in wrong which can cause that also, but I have never actually seen it myself. What I have seen is blockages from the line, such as teflon tape, or other debris; as well as blockages from the valve such as a torn o-ring. If this valve has been installed a long time and has just recently stopped allowing hot water to flow, it is possible that hard water buildup is the culprit.
In pretty much every situation, if there is hot water flowing to this valve, changing the cartridge and cleaning out the valve body while the cartridge is removed will solve the problem.
Turn off the house water, remove the cartridge, turn on the house water for one second and then off again (to clean out the valve body), then install the new cartridge and test.