Rumbling pipes

[Lenn G]

Hello

My parents neighborhood was recently required by the town to convert from private well water to town water. The water supply was converted in the summer of 2011. In December my parents called me to tell me they heard a 10 second rumbling noise from the unfinished basement every couple of minutes. With me helping them on the phone we narrowed down the noise to the somewhere with in the cold water pipes. They called in the plumber that did the conversion to look at the system, but they could not recreate the problem and so he could not find anything wrong.

Last weekend i was my parents house and the problem happened again . This is what i found in the morning when very little water had been used. The rumble was about 7 sec long and repeated approximately every 2 minutes. The vibration was definitely in the cold water pipe more noise and vibration on the far end of the line at the bathrooms. I tried various ways over 20 minutes to isolate the problem but i could not find any clues. The problem did go away when the kitchen sink was running for about 10 minutes while washing the dishes. Any ideas how to eliminate this problem.

Regards
Lenn G

[SteveW]

Do a search on this site on "thermal expansion" and see if this fits.

I had similar noises in my previous house and that's what it was. The key is that it only happens after a volume of hot water is used in a short time, then no water is used while the water heater is heating up the cold water replacing that which is used.

[Lenn G]

Thanks for the feed back Steve, I will do the search. Basically you feel there maybe some pressure building in the system when the hot water tank is heating the water creating the rumble. Do you know if there should be any modifications to the system when you switch from well water to city water hook up. Or do you think there is no connection between the rumbling and the new city water. I did see well tank was removed and a small expansion tank was added to the system.

Much Thanks
Lenn G

[jadnashua]

Have them pick up a pressure gauge with a second tattle-tale hand to show peak pressure. Many new water connections will have changed the home's piping from an open system to a closed one. The bladder well tank (which is probably no longer connected) gave expanding water a place to go. For safety purposes, many new installs put a check valve on the inlet from the street. So, without an internal place for expansion when heating water in the tank, it can increase the pressure rapidly. It will then leak out the weakest link, which is often the toilet fill valve, or if it gets high enough, the safety valve on the WH (the T&P valve) will open to relieve a small amount of water which reduces the pressure.

The second hand on the pressure gauge will show the peak pressure, and you can read the instantaeous pressure off the main hand. Cost is only in the $10 range, and you can screw it into a hose connection (say the washing machine, a hose bib, or anywhere with adapters).

If the static pressure is over 80#, then they also will need a PRV (pressure reduction valve) and if there is a check valve now, or you add a PRV, you'll need to have an expansion tank installed.

You could try shutting the supply to the toilets off temporarily to see if the noise stops - they are a fairly common 'leak' point if you have high pressure, and some of them can be noisy when that happens. They should be okay if the pressure stays below 80#, though.

[SteveW]

What Jim said.

I have always been on city water but I had this happen to me, from the check valve in a pressure-reducing valve. Made a strange groaning sound at night, after we used a batch of hot water then went to bed, so the water heater heated the incoming cold water, which expanded but had no where to go so put a lot of strain on the pipes.

As Jim says, if you have this situation (thermal expansion), you will need to put in an expansion tank.

[Lenn G]

Guys

Thanks for the inputs i will check into a gauge to monitor the pressure. In the change over the plumber did install a small expansion tank (Watts PLT5). This tank is located on the incoming water supply. Do you think a second tank would be need on the hot water after the hot water tank ??

[jadnashua]

No, the expansion tank is where it's supposed to be...they don't last long if put on the hot side. Watts has a calculator on their website to determine the needed size - bigger is okay. Plus, you need to double-check that the precharge on the tank is set properly. While not particularly common, it's possible the tank is bad. you need to shut off the water, open a valve to relieve any pressure in the system, then you can check the precharge on the expansion tank. It should be about the static pressure of the water supply system, so you'll need the gauge first. Then, if the house water pressure exceeds 80psi, they should install a PRV, or fix the one they have (usually cheaper to just replace). The safest way to add air to the expansion tank is with a bicycle tire pump - if you use a compressor, be careful not to overfill it.