Similar to many other postings, with one twist, I have experienced a sudden loss of hot water pressure throughout my 2006 home. Without warning, hot water, when called upon at any fixture, will run for a second or two, then pressure falls to zero. If I close the faucet for a few moments, pressure builds up and when I open the faucet again, high pressure hot water flows for couple of seconds as pressure again falls to zero. This has gone on for a few minutes in some cases to several hours in other cases. Upon some random opening of a hot water faucet, I'll hear a loud bang, which I assume is some sort of water hammer event, then the hot water works fine until the next random event. I've read other postings which talk about a stuck check valve, which makes perfect sense, but I haven't a clue where a check valve would be located, except for internal to the hot water heater.

Sounds more like a problem in the cold water input valve to the water heater. Could be a loose washer but sounds more like a blockage. If it is a blockage, it is likely a piece of solder that is lodged in the valve. When sweating copper pipe (I am assuming copper) if you use too much solder it can run inside the pipe, only later to break away and lodge in the next available valve. I would change out the stop valve on the cold water input to the water heater.

If you have heat traps installed it could also be a sticking heat trap. If you indeed do have heat traps, the next time you loose water pressure, tap on the side of the heat traps to see if it breaks loose.