water hammer with new bathroom plumbing

[theHammer]

My bathroom was just completely redone with a new (Toto) toilet, new sink, and new bath/shower. The shower has a single shower mixing valve - our (very) old bathroom had separate taps for hot & cold and bath & tub.

We noticed that if we have the shower set to a comfortable temperature, when the toilet flushes we hear a hammering noise that comes from violent shaking in the cold water supply line. The noise starts as soon as the flushing starts and continues even after the toilet refills and shuts off.

Closing down the toilet supply line valve slight will prevent the problem from occurring.

However, shutting off either the hot or cold water in the sink will ALSO cause the problem to occur. Putting the water back on stops the banging. If the water in the sink is turned off very slowly, then the problem does not occur.

After reading many of your previous postings on problems like this, I am not sure whether the problem is most likely to be a defective or stuck mixing valve (it is brand spanking new) and/or just poor plumbing.

The cold water supply line comes up to the bathroom to a T just above floor level. At that point one line goes off perpendicular to the wall to supply the shower valve. When it reaches a point below the valve it turns vertically and goes right up to the level of the valve where it makes one more turn to attach to the valve.

The other line at the T continues straight up for a foot or so and then jogs an inch or two away from the wall and then turns to run parallel to the wall to supply the sink and then the toilet. It passes through a hole in a stud which is where the vibrations appear to get amplified. I have seen that I can cut back on the intensity of the banging by stuffing something soft around the pipe where it passes through the stud, but that doesn't really solve the problem since there is still a lot of noise and the water pressure still fluctuates rapidly in the shower.

What do you suggest?

[jadnashua]

Did you reuse the shutoff valves? Or, if not, did you use the multi-turn or 1/4-turn valves? The washers in an older style multi-turn shutoff can sometimes flutter and this movement can cause variations in water flow making some nasty noises. SOmetimes, it's as easy as replacing the shutoff or putting in a new washer in the old ones.

[theHammer]

I am not sure which shutoff valves you are referring to, but nothing was re-used. This was a complete bathroom renovation - down to the studs. All new pipes, walls, floor, fixtures.

[jadnashua]

The shutoffs for the toilet and under the sink...also, some toilet fill valves can create noise problems. Do you know what kind is in the toilet?