Each condo unit has its own water heater and boiler, but we share one water source. The water also passes through one comon water softener. I had my water heater replaced in March and a new sink installed in the kitchen in May (not sure if either is related, since the banging just started).

There isn't an exact pattern to when the banging starts and stops. The first time it started in the middle of the night. Sometimes, though, it clearly begins when I use water (when I get home from work, up in the morning, run the washing machine). The first time I was able to stop the banging by running the Temperature-Pressure Valve on the water heater. This temporary fix has not worked since then. Usually the banging stops after a while, but it continued all night last night. I've also tried turning off the water at the bathroom sink and toilet to see if the noise stops, since the banging frequently starts in the morning before I've used the shower. This has not stopped the banging, either.

I spoke to a plumber and he theorizes that I need a new reducing valve. Since the 4 units share one water source, I asked him why the other units would not have the same noise. He said that the lower floors would have the most pressure (I am basement/ground level...the house is built on an incline). He said the other units might never experience the noise, even though it is a problem at the source...not at the individual unit level. I should mention also that his company installed my water heater. My father disagrees with his statement about varying water pressure on different floors of the building. He is concerned that I am being persuaded to purchase something I don't need (the reducing valve was quoted at $275-$475 installed).

Does it sound like I need a new reducing valve? Is there anything else I can do to try to figure out what the problem is before I have a plumber come?