Charlie: “Jessie in Pearland says: “I have a knocking sound that appears to be from the wall-”
Tom: “Go answer the door. No, don’t answer the door.
Charlie: “Anyway, “I have a knocking sound that appears to be from the wall of my bedroom closet every time we flush the toilet, shower, wash clothes, or use the dishwasher. Could you tell me what it is?”
Tom: “Probably just a water hammer. I don’t know if any work has been done on the house lately, but what you do is you turn the water off to the house, you open up all the valves, try to drain all the pipes, then close all the valves nice and tight and turn the water back on. Your chamber in your riser will fill with air like you want it to because it’s your little shock absorber, and it will hopefully take that away.
Now, if it’s when something is running, you could have a loose washer somewhere that’s banging around. If it’s happening in a sink or something and you hear this knocking sound … But it sounds more like a water hammer to me. It’ll be one of the two.
Charlie: “So, let me get this straight. You turn the water off to the house.
Charlie: “Open all the taps.
Tom: “Yes, drain the pipes. Yes.
Charlie: “Turn the water back on, and then turn off the taps.
Tom: “No. Turn off the taps, then turn the water back on. Reverse the last two.
Charlie: “Oh, okay. Got it.
Tom: “You want to force the whole thing full of air first, and it’ll spit a little bit. Don’t worry about that, but you want to fill those risers with air. They probably got full of water.