faucet
I have erratic hot water from my tap in the bathroom sink, when I turn on the hot water it runs for about 30 seconds and then bangs and the water stops. After a few seconds the water returns with a force and we have a constant banging like a machine gun, from the tap.
What could cause this, and how can I fix it?
From your comment, it sounds like the root issue is the lower water pressure from your hot supply. With lower water pressure, when you only slightly open the valve, there might not be enough pressure and/or flow for the water to overcome the other forces acting against it (gravity, restriction from valve, etc.). Similar to say a garden hose - with low pressure, it might not leak at all, but open the valve up all the way and it starts leaking at certain places (except in this case, the leak is the flow you want).
The first thing to check is that the shutoff for your hot water supply is fully open - at the sink, at the tank and anywhere else along the way where there might be a shutoff. If all of the shutoffs are fully open then it could be due to incorrectly sized pipes, mineral build up (depends on type of pipe). Check to see if the pressure is low at any other facuets - this will give you a good idea if its a problem with the plumbing or just that particular fixture.
Very small pieces of debris (very frequently rust chips in homes with older galvanized pipes) can block one side or the other of the cartridge of a shower valve.
Newer valves have replaceable cartridges than can be examined and cleaned. Just shutoff the water, open and close the valve to relieve pressure and undo the trim plate.
Note, examples are of Delta shower valves
The Cartridge is usually behind a finely threaded retaining nut (bonnet nut).
Sometimes the seals break and jam.. here's a Delta cartridge and seals
Best Answer
You've got a bad valve causing the water to stop. You may be able to only replace the cartridge/valve inside the faucet to solve the issue, but keep in mind that this could also be the shutoff under the sink. As user663387 says, the banging sound is water hammer, but I suspect that's an effect rather than the cause.