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Q.I am having a problem with a shower valve in a bathroom remodeling project. When you turn the water all the way to hot and then back off to around the middle of the temperature range, you get a pulsating water flow from the shower head and severe, loud knocking from the shower pipes in the wall. The problem does not occur when the valve is opened all the way, full hot. We've secured the valve and the piping with clamps. Are you aware of any remedy for this problem short of taking the tiled walls apart to install a water hammer arrester?

A.Master Plumber Rex Cauldwell responds: A water hammer arrester won't solve the problem; I think the problem is in the faucet body itself. This type of water pulsation and the associated water hammer are typical of faucets with balancing valve assemblies and check valves. The problem is not limited to one manufacturer; I've experienced it with several brands.

You have a choice of pulling the valve cartridge and checking it for debris or just replacing the faucet. Most of the time, I replace the faucet, because, even with new parts, I often can't fix the problem. I typically switch the faucet to a Moentrol, by Moen (800/289-6636,; I've had the best luck with that brand.