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Rick
Rick , General Contractor
Category: Home Improvement
Satisfied Customers: 18714
Experience:  Licensed construction supervisor with 35+ yrs. experience.
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A plumber replaced the old fixtures on my bath tub, shower,

Resolved Question:

A plumber replaced the old fixtures on my bath tub, shower, and hand basins when I was doing a major M/B refurbish and replaced them with new ones. I now have knocking only when the cold water is shut off.
We have done EVERYTHING for one whole year, called the plumber back who left me with torn out walls and 2 hours later could not find the problem.
1) We then turned the mains off drained every faucet and there was a slight improvement, but it just came back.
2) We turned off the mains, opened every faucet drained them left them on and turned the mains on, that made it worse.
3) We repeated step one.
4)We then fitted 4 of those regulators by the shut off valve, in the bath tub and wash basins, didn't work, so we took them off.
The only thing which has made a slight improvement is:
5)We turn off from the mains and then run out the water from the lowest faucet ONLY (we do not drain out the others) until completely drained and then turn the water back on very slowly and there is an improvement, but the knock eventually comes back.
we have been trying to figure this out and for one year! can you help?!
Submitted: 2 years ago.
Category: Home Improvement
Expert:  Rick replied 2 years ago.

Rick :

Welcome, my name is XXXXX XXXXX I will do my best to help you with your issue.

If the knocking is a single bang/knock then you probably have a water hammer condition and installing water hammer arrestor(s) (basically a shock absorber) on the water line to the shower should solve the problem. If the knocking is a series of knocks then you probably have a defective cartridge in the new shower valve. Replacing it will probably solve the problem and since the valve is so new it should be under warranty so you should be able to get the part at no charge.

Customer:

as i said we tried the hammer arrestors and it made no difference and we also tried a brand new shower head and the a shower valve, still did not make a difference!

Rick :

I didn't see any mention of water hammer arrestors

Customer:

Oh so sorry did not mention them because i could not remember their name. we put 4 on: 2 on the tub and 2 on the hand basins

Customer:

Oh so sorry did not mention them because i could not remember their name. we put 4 on, 2 on the tub and 2 on the hand basins

Rick :

What is your water pressure?

Customer:

and i did not mean to enter that 3 times:(

Rick :

No problem

Customer:

i'm not sure, however this house is a 1978 and when we bought it there was no problems for 2 years, this only happened after the plumber came.

Rick :

Well, excessively high water pressure can also cause this problem. There is no explaining why this is a new problem. I'm assuming we're talking about a single knock when you shut the water off

Customer:

by the way we did reduce the pressure by turning the shut off valve to less pressure and it does not go away unless there is a dribble of water.

Customer:

and yes it is one knock

Rick :

Throttling down the shut off valve won't affect the water pressure. It only affects the volume of water flowing

Customer:

yes this is also making us pull our hair out because nothing logical is working

Rick :

Is this from both the sink and shower cold water?

Customer:

OK but if there was no problem before the plumber, but only after he changed out the faucets...

Customer:

yes

Customer:

and the tub

Rick :

Like I said there is no explaining why you didn't have this problem before except perhaps that now you have faucets that shut off quicker. You need to check the water pressure since it''s the only variable you haven't looked into yet. It must be below 75 psi.

Customer:

OK how do i check the water pressure

Rick :

You have to put a gauge on the water line. The easiest way to do this is on an outside faucet. You can either buy a test gauge with a female garden house fitting attached or you can make one up with a water pressure gauge and a 1/4" female X female garden hose adapter. You screw the test gauge onto the outside faucet then turn it on

Customer:

OK Rick we will try this tomorrow, if it is 75 psi can i get back to you?

Rick :

Just post to this thread. It won't go away even after you rate me favorably

Rick :

You can get back here by logging back into your account

Customer:

i'm not savvy when you say get back to this thread but I'm sure my husband will be able to. thanks

Rick :

You're welcome. All you have to do is log back into your account here and you'll see a link to this question. Or you can just bookmark the page

Customer:

by the way if it is too high how do we reduce the pressure?

Rick :

You have to install a PRV (pressure reducing valve) on the water main

Customer:

Ok i will get with my husband who hates plumbing and this on going problem and see how the pressure is many thanks.

Rick :

My pleasure

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