at a natural gas water heater. It is not the sound you get from buildup at the bottom of the tank. It sounds like someone is hitting the pipes with a small metal hammer. If you put your hand on the pipes you can feel the shock vibrating the pipe. It happens late at night when there has been no use of hot water and the burner has not been on. If the main supply ball valve to heater is turned off, the noise stops. Sounds like it is pressure related. Ideas, suggestions, buy a new house?
Thanx in advance.

 

:ibmovetoH&G:

Sounds kind of like air pressure build up in the pipes, but don't understand the connection to the water heater. Does it happen when you turn on/off a faucet?

 

No it is not "water hammer" when a faucet is opened.

 

I think I might know the fix to this. I saw it on This Old House.

First of all, if pressure is building up in your tank the pressure release valve is supposed to open and spill water all over your floor. So the first thing you need to do is make sure that valve is working.

Anyway, when you heat up water you build up pressure. In older houses that excess pressure is pushed back to the water company. However that can pollute the water system if your tank has rust or other issues. So code in some areas doesn't allow the pressure to go back to the water company. So where is the pressure to go? It tries to go into your house. When the path is blocked it blows your pressure relief valve and you get water all over the floor.

The way to stop the pressure relief valve from blowing is to have a plumber (or you) install a pressure relief tank. The tank looks like something you would stick on a gas grill. The tank has a bladder in it so it can't fill completely with water. You basically get a tank with half water half air.

You can test to see if you really have a pressure problem by sticking a water pressure gauge on your tank. I don't know what the normal values are but I suspect google does. Stick it on there while the heater is off and then watch to see how high it goes up when it turns on.