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This happens on every faucet in the house. Sometimes, when you first turn on the hot water, it comes out (just the pressure in the line) and then it runs slow and stops. Then, a banging noise happens and the water starts. At other times, there is a banging noise at the time the hot water faucet is turned on. More recently, there is a slight banging noise in the pipes after flushing the toilet (which is cold water). I have tried reducing the water temp on the hot water heater. I considered buying a water pressure gauge to see what our household water pressure is. Is this a problem with the entire water system or perhaps the hot water tank pressure regulator?

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You get a bang when you turn a faucet on??? That's not water hammer, water hammer happens when a faucet or other valve (like a toilet's float valve) turns off. – TDHofstetter Aug 23 '14 at 12:47

Likely problems

  1. Over-pressure from the street. Solution is installing a pressure reducer just after the main shutoff.
  2. Missing or leaking "water hammer arrestor", which is a vertical pipe with air in it or a tank with an air bladder, meant to soften sharp pressure changes.

Water temperature is not a likely candidate except at the extremes. If you have a local tool library, or perhaps home store, they may loan out pressure gauges.

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I've experienced symptoms similar to this in the past, and the culprit turned out to be a failing pressure reducing valve. It wasn't holding back the high water pressure from the municipality so high water pressure could be measured inside the house. Look for a bell shaped object after your main water shutoff. Replacing this valve, and also adding an expansion tank, resolved this issue in my scenario.

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Normally you associate a bang in the pipe due to water hammer but that occurs on faucet turn off, however if the temperature in the heater gets high enough to create steam the steam will locate at the top of the tank so when you turn on the hot water faucet the steam then enters the line and can make a noise so first thing to do is run the hot water at a point closest to the tank and measure the water temperature....easy to do. Temperature must be under 140 degrees and more like 130 for safety.

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I doubt the OP would have missed the fact that the hot water tap was emitting almost-boiling water. – Daniel Griscom Apr 16 at 2:51

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