I really need to find a solution. Shower taps- two separate- not a mixer. There was a slight hammer as I opened the hot water and as i closed it. I swapped the taps over and secured the pipes so there’s no movement. Still a small thunk as I close or open the tap but not as bad as before.
The system is; hot water and cold water come in to two separate taps. The water goes through the taps and connects to one pipe that goes to the shower head. Pretty standard. The issue is that after opening the hot water a couple of times, the tap can be opened all the way and no water comes out. And stays like that. I can open it fully and close it again multiple times and no water flow. How is that possible? The cold water tap works fine even though it was the tap that was on the hot side and did exactly the same thing before I swapped them over.

I'm going to guess that the valves use a washer to control the water flow and those washers are bad. The hot water flowing through the pipe and passed the washer, Heats up the washer, softens it, causing the problem. At a minimum, change the washers.