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aplnub · Apr 16, 2010, 07:11 PM

I have copper lines in our house. Walk out basement with living space above. House was finished in 2003.

I have a hot water circulating pump to keep the water warm in the hot line for fast hot water. I also have a thermal expansion tank installed and was properly charged with air before turning the water on. I have also recently replaced my PRV (pressure reducing valve) to eliminate a bad PRV.

We have 105 psi coming into the house and after the PRV (which is inside the basement where the water comes in) I have 55 psi. I have gauges permanently mounted on both sides along with shut off valves.

Problem
After relocating the hot water heater from the inside finished part of the basement to the unfinished side we noticed a "hammering" sound that occurred when any fixture in the house was turned on. At first it was for a second or two. Now, it may last 45 seconds or until the water turns off.

Seeing how it is not water hammer, my first reaction was to get up in the floor trusses and find a loose pipe while the sound occurred. It sounds much worse upstairs than down stairs for some reason. I then purchased copper straps and screwed down every cold water pipe I could find, loose or not.

No change in the problem but it is getting worse little by little.

We have opened all fixtures and turned off the water coming into the house in order to drain all the lines and to hopefully recharge the stand pipes behind the shower. This works for about 6 hours and then the problem is back.

Does anyone have any idea what in the heck is going on with our situation? I have never seen anything like this in all my life and neither has anyone we have brought over to listen and witness the problem. Everything was fine until we relocated the hot water heater but I cannot see what problem that is causing because it ONLY happens on the COLD water. Still, the two must be related.

InfoJunkie4Life · Apr 16, 2010, 08:12 PM

Could be an air bubble trapped in the line somewhere...

hkstroud · Apr 16, 2010, 09:06 PM

My first thought would be the PRV valve. Sounds like it is rapidly opening and closing, causing a water hammer sound. Logic for being cold water only would be that the volume of water in the water heater is acting like a cushion and counteracting rapidly changing pressures.

This could also be caused by a loose washer in main shut off valve, with no explanation of why its cold water only. Try partially closing main shut off valve a turn or two.

aplnub · Apr 17, 2010, 07:13 AM

Originally Posted by hkstroud

My first thought would be the PRV valve. Sounds like it is rapidly opening and closing, causing a water hammer sound. Logic for being cold water only would be that the volume of water in the water heater is acting like a cushion and counteracting rapidly changing pressures.

This could also be caused by a loose washer in main shut off valve, with no explanation of why its cold water only. Try partially closing main shut off valve a turn or two.

I will try partially closing the main shut off valve we have inside our home. We ruled out the PRV by changing it. They normally give a humming sound when bad.

I am up for anything these days because it has been driving us nuts.

speedball1 · Apr 17, 2010, 07:24 AM

Where do you feel the vibration the strongest? What PSI did you charge the expansion tank at? Cheers, Tom

hkstroud · Apr 17, 2010, 07:37 AM

Just for grins, close the stop valve at all toilets.

aplnub · Apr 17, 2010, 07:48 AM

I have a Watts 25AUB PRV in case it matters. That was also the previous model I had before changing out the new one a few weeks back.

Let me correct one thing, our pressure inside the house is at 50 psi. I read the gauge incorrectly late last night.

I initially charged the thermal expansion tank to 50 psi (matching the water pressure per the Watts TE tank instructions). Just to be sure the tank, which is new also, did not have a burst bladder, I shut the water off to the house, opened up the lowest (elevation wise) fixture, and drained the water so the pressure in the lines would be zero.

I then took a reading with a tire gauge at the bottom of the thermal expansion tank. 50 psi was the reading.

I then turned the water back on and took another reading to make sure the gauges were reading correctly. 50 psi again.

aplnub · Apr 17, 2010, 07:53 AM

Regarding where we believe the vibration is the strongest. My wife and I debate this so here is the low down.

She believes is the part of the house that is over the current hot water heater placement.

I believe the noise to be the loudest over the washroom or closest to the location of the previous placement of the hot water heater.

I have crawled up through the floor trusses, not fun, and followed what little plumbing we had in those areas. When the noise is happening, there appears to be zero pipe vibration by looking and feeling. Also, I screwed everything down a little tighter just to be sure. Probably not the smart move but it was the cold water line so temperature change from the incoming main is not great (I actually work for the water utility that provides us with drinking water).

One last thing, this happens sporadically. We may go 3 hours without it happening and then it happens three times in a row. Normally though, once we have a large episode, they weaken for a time.

Whether it be the kitchen sink, master bath shower, any toilet, washing machine, or outside spigot, it happens. I can record the sound if anyone thinks that would help.

I have had everyone over to diagnose the problem and we have yet to do anything that has seemed to make any difference at all.

hkstroud · Apr 17, 2010, 07:57 AM

Can you show a picture of expansion tank?

aplnub · Apr 17, 2010, 08:10 AM

Originally Posted by hkstroud

Can you show a picture of expansion tank?

Below you see the setup. Incoming from right to left in photo. The thermal expansion tank is within three line feet of hot water heater in one of two approved positions per instructions.

Close up photo of tank. A Watts PLT-5

Close up of directions that came with tank.

Incoming line showing gauges. Before anyone says anything, I know I have two galvanized fittings there. I am changing them out this weekend. This is the only galvanized I have in the house and that was not even supposed to happen.

hkstroud · Apr 17, 2010, 08:22 AM

Don't see anything in installation instructions but logic says that if there is no bladder in tank it would have to be mounted above the piping. Otherwise the air in the tank would be pushed out by the water, making it ineffectual.

Either close the cold water input valve to the water heater or turn water heater off for period and see what happens.

Do you have check valves on recirculation lines? How about remove pipe insulation and let us see you set up. Doesn't look right to me.

aplnub · Apr 17, 2010, 08:26 AM

Originally Posted by hkstroud

Don't see anything in installation instructions but logic says that if there is no bladder in tank it would have to be mounted above the piping. Otherwise the air in the tank would be pushed out by the water, making it ineffectual.

Either close the cold water input valve to the water heater or turn water heater off for period of time and see what happens.

Do you have check valves on recirculation lines? How about remove pipe insulation and let us see you set up. Doesn't look right to me.

The tank has a bladder. No doubt about it. I had the same model before and I cut it open to see for myself when the last one failed.

What does not look right in my installation?

Yes, I have a check valve in my recirculation loop for hot water.

hkstroud · Apr 17, 2010, 08:31 AM

Maybe it's just the pic. Does recir line tie back into cold water input? Tap expansion tank with wrench, bet you get the sound of tank filled with water.

Shut down water heater for period and bet a pizza your jack hammer goes away.

aplnub · Apr 17, 2010, 08:32 AM

I think I found what you thought looked wrong.

My thermal expansion tank is in the loop!

There is a check valve preventing hot water from flowing back into the cold water.

This may explain why the beating noise happened after the water tank removal.

I'll get this corrected promptly. An oversight by my plumber I am sure. I can't believe I didn't catch this myself.

Thanks, and I WILL report back.

aplnub · Apr 17, 2010, 08:36 AM

Originally Posted by hkstroud

Maybe it's just the pic. Does recir line tie back into cold water input?

We posted at nearly the same time.

Also, above when I said removal I meant relocation.

But yes, you are correct, the TE tank is in the hot water loop.

This must be what is happening:

Open cold water fixture.

Cold water flows out of fixture creating a bouncing effect on the check valve creating the problem we hear. It means my wife's hearing locator senses are better than mine :( but I will take it if it means getting this fixed.

Thanks so much guys. I will be in touch again.

hkstroud · Apr 17, 2010, 08:43 AM

My logic may be incorrect, did the old tank you cut apart have the input piping to the bottom of the tank?

Edit; Sorry, misread you post as your tank definitely did NOT have bladder. Sorry

aplnub · Apr 17, 2010, 08:50 AM

Originally Posted by hkstroud

My logic may be incorrect, did the old tank you cut apart have the input piping to the bottom of the tank?

To be honest, I can't remember and I recycled it several months ago.

Even though we have figured out that my TE tank is in the loop, which means that it is not working at all since it is not connecting on the cold water side, I am assuming that the TE must act has a water banging snubber since we did not have this problem before.

hkstroud · Apr 17, 2010, 08:58 AM

The tank allows water in the heater to flow back into the cold water line as it is heated and expands. Pressure in the heater cannot be relieved through the hot water side because all the hot water faucets are close. The PRV prevents the back flow into the cold water side so the expansion tank is required to hold the water.

hkstroud · Apr 17, 2010, 09:12 AM

Just for you information. I have a 2 story home with water heater in the basement and a recirculation line.

After a few years the recirculation pump quit. I cut the pump out and repiped temporarily, pending replacement of the pump.
Found the system stilled worked. Apparently the hot water rising, cold water water falling, and the siphoning action caused by the cold make up water passing the recirculation line connection keeps the circulation going. No pump used.

hkstroud · Apr 17, 2010, 09:33 AM

Are you sure that the expansion tank in in the hot water loop? From pic it appears to be on the same pipe as the cold water shut off valve.

Here I go trying to be logical again.

You said you have a check valve on the cold water input to prevent recirculated water from entering the cold water pipe. Where is the check valve? It has to be located up stream of the expansion tank. Otherwise the expansion tank cannot do its job.