I have a shower that doesn't get a lot of use in my house, but recently, we recaulked our main bathroom, so I was planning on using that shower. It has a single turn knob for flow and temperature, and when turned past cold to the hot side, the flow is reduced to barely a stream, not even enough to keep the shower tab up, but the water does get hot. Could it be the shower valve?

Thanks in advance for any help!

You mention a "shower tab" . If this is the tab on the diverter valve (tub spout), how is the water pressure & temperature coming through the tub spout when filling the tub? While the "shower valve" is the most likely culprit, there could be a problem with the hot water supply line coming to that valve. The valve can probably be dis-assembled & cleaned if it is clogged. Replacement is the final answer.

Please post the brand and he model number of your faucet, it sounds like there is some debris in hot port inside the faucet, needs to remove the cartridge clean or replace the cartridge and flush the faucet, if you post the info some one will help you, thank.

John