I have a single knob on my bath tub that controls the hot and cold water. The cold water will come out, but the hot water will not. Please help! No hot water at all only cold water when the knob is on H & C.

What's the brand name of your faucet? Your hot water inlet ports in the cartridge are clogged and must be cleared. Shut the water off to the valve and open it up. Clean the inlet ports on the cartridge and before you button everything back up turn on the hot water for a second to flush out the hot water supply and valve body. Good luck, Tom

The brand name is called Moen. I took the screw out and I am looking at the Moen Rough-in Posi-temp Pressure Balancing Cycling Valve. Do you think this needs to be replaced?

Here is picture of the valve that I am looking at.

Here is picture of the valve that I am looking at.