Water hammer problem
Last year I had an upstairs bath remodeled. Since then, there is a water hammer somewhere, whenever the water is turned on/off anywhere in the house. Can't tell where. Years ago, this was a problem in a former house and the plumber told us to do something that fixed a similar problem, but I can't remember. He said something like we need to get air back into someplace in the piping designed to "cushion" the pipes under pressure??? So he had us either: open all the valves and turn off the water to the whole house, OR turn off the water at the main, then open all the valves and turn on the water at main then close all the valves, OR turn off water, open all valves at once, then close and then turn water back on. It worked, whichever it was. I notice last week that our water was off because of a power outage (am on a well) and I opened several faucets, just out of habit to draw water or wash hands and nothing but air blasted out. When the water came back on, the hammer was fixed. YAY!!! But now, slowly it has returned. Any ideas the reason/problem/solution?