If you turn on the hot water in the shower the pressure is low and then clanking sounds and then no water out of the faucet Hot water works weel in the sink and kitchen. If you turn on the shower head and then open hot water its OK

If you turn on the shower head and then open hot water its OK This tells me that you have some crud in the valve that's blocking the flow. To tell you more I'll need the type of mixing valve that you have. One handle or two knobs?The brand name. It's age. And any other details that you can furnish. Waiting on your reply, Tom

I have this same problem... no hot water pressure in the shower... first it was the bathroom sink, now the sink is fine. The faucet setup is two knobs. There is no discernable information on them. They look pretty old - definitely nothing fancy. What is a mixing valve? I live in a condo... is this important in the scheme of things? The water pressure is fine in the rest of the condo. Though it seems the water pressure has been generally inconsistent over the four years I have lived here and in different areas. Thanks! Tracey