This is a long description but I'm desperate:

We installed a new water heater 6 months ago. Just to give you a mental picture: we live in a townhouse where the water heater is in a closet right next to a bathroom on the second floor, and the main water line (with a pressure regulator) is on the first floor. Ever since the installation, we hear a hissing sound in the bathroom followed by water that gets discharged into the toilet. We didn't think anything of this until 2 weeks ago, the hissing sound was shortly followed by a loud bang and then the water discharge into the toilet. This loud bang would only happen when we don’t use the water (hot or cold) for awhile (2+ hours). Otherwise, if we do use the water, only the hissing + water discharge. So, since the only time we won’t use the water for more that 2 hours is during the late evenings when we’re asleep, we get jolted awake by this loud bang. We installed a thermal expansion tank (it’s right next to the heater) thinking that it would fix the problem but the problem went from a loud bang to being a loud rumbling/rattling noise. I also noticed that after awhile, the cold water pipes leading into the water heater gets hot, as if hot water is going back in the cold water pipe, and the expansion tank remains cool. But after the rumble+hiss+discharge, the cold water pipe is cold again. The plumbing company that installed the water heater and expansion tank said it has nothing to do with the heater and advised us to shut the water off leading into the toilet to see if this still happens. My thoughts are that if the problems is with pressure and the toilet is acting as a relief point, of course shutting it off will stop the rumble+hiss+discharge, but wouldn’t all this get built up in the pipes and eventually something’s got to give? Can we never use that toilet again? Please, any advise would be very helpful on what might cause the loud noise and how we can fix it.

I think your installer is all wet. The chances are high that his heater and expansion tank are causing/ allowing a high pressure to build in your plumbing. Ask him/tell him to get himself out to your home and do a pressure test, 45 psi is pretty much optimal.

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Originally Posted by ballengerb1

I think your installer is all wet. The chances are high that his heater and expansion tank are causing/ allowing a high pressure to build in your plumbing. Ask him/tell him to get himself out to your home and do a pressure test, 45 psi is pretty much optimal.

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Thanks for the quick response. When they installed the expansion tank, they first took a pressure reading from the hose faucet on the first floor. It read a little under 120psi when he first turned it on. However, we advised him to let it run for a little bit since the pressure tends to diminish. After doing so, the reading went down to a little below 50. Prior to their arrival, I had modified the pressure regulator hoping that by reducing the pressure, the noise would go away. But the reduced pressure made the showers and bathrooms on the top floor basically trickle. After they installed the tank, they increased the pressure to around 58. I guess when the water system isn't being used, the pressure increases to over 100, but the minute we use it, it drops. I've been doing some reading on various sites and I'm wondering if I might have water hammer caused by a quick closed from our toilet. I'm thinking of replacing the flush valve (which is a anti-syphon Fluidmaster from HD) with a Watts Governor 80 that has a pressure relief system. Do you think this might help?

I just want to add that before going back to the plumber that installed our water heater, we asked another plumbing company to have a look. They indicated that installing the exanpsion tank and changing the toilet valve would fix the issue. Do you think this is true?

It sounds to me that the pressure reducing valve is not operating correctly. It should drop the line pressure coming into the home to about the 45-50 range and not allow it to raise higher even when no water is being used, the expansion tank should absorb the pressure of water being heated in the water heater. Once you crack open a faucet the PRV should be able to keep that psi pretty much constant even with an increased volume/flow. Didn't they check the PRV for you? What PSI does your city water department claim they maintain? Why would the other company want to change the toilet? Don't work with those guys either, at worst you may have a weak diaphram in the ballcock but a new toilet??

They indicated on our receipt that the PRV may possibly need to be changed. I'm not sure what PSI the city maintains. Would I ask the water supply company of check with the city? Actually, it's not the toilet that they wanted to change but the flush valve.

Yes you can call the city water department to ask the psi in the main. You can then also ask them to come out to your home and verify, sometimes it's their fault. Flush valve I could see maybe but lets see what the city has to say. It does appear that replacing the PRV is in order but also wait for the city, they might help you solve the issue.

Thanks ballengerb1! I'm going to call the city water dept. One last question for now, do you think we should leave the water line to the toilet turned off?

Yes, I'd tempoarily shut off the stop cock below the toilet. The tank will be full so you get one good flush. You can always turn the valve back on/off to refill the tank on the toilet. Chances are slim that this is totally needed to prevent a flood but why take the chance.

Hi ballengerb1,

I attached a pressure gauge to the water hose faucet and it initially showed 80 psi. I then let the faucet run for about 15 seconds and took another reading and it showed a little over 50 psi. I know you indicated that the PRV shouldn't fluctuate and it should keep the entire home at a consistent pressure. Do you think that the PRV needs to be repalced?
Fyi - we left the toilet valve off last night and for the first time in days, there was no banging/rumbling noise. I’m wondering what is now happening to all that pressure that use to get relieved into the toilet? I’m also guessing that the banging was from water hammer of the water getting released into the toilet as well. We’re a little worried so we’ve taken to shutting of the main water line when we leave for the day because we’re afraid of any pressure buildup that might happen throughout the day.

The PRV needs to be changed.

Hopefully the expansion tank is on the cold water side of the water heater.

Lets wait and see what the city water department tells you before you spend money on a new PRV.

HI ballengerb1. Ok, so the water company that services our development area dropped by and said the water level coming into our home is a consistent 75psi. They indicated that if there was an issue with the water pressure being too high, then it wouldn’t just effect our unit, but our neighboring units as well since we’re right next to each other. We described the issue of the water pressure being very high when we initially open the faucet and then tapering off to a consistent flow after a few second and they believe this is normal. So, at this point, do you think it’s worth changing the prv?

Thanks.

Yes and I don't like those guys from the water department. I was hoping/expecting them to admit 75 psi is high and offer to install a PRV for you at their expense. Too much to hope for I guess. I would replace the valve with one that brings your pressure done to a consustent 45 psi.

Hi ballengerb1,

Just wanted to let you know that everything appears to be fine now. We had the PRV repalced and, although the plumber has kept the pressure at a high level (65psi), at least the pressure is now consistent throughout the home. He also replaced the valve that turns the water off to the toilet (at no charge), so we haven't been experiencing any problems there. Also, he find out that the hissing and water releasing in the toilet tank was due to a defective flap that was causing the tank to drain very slowly. I replaced this myself and it fixed the problem.

Thanks for your advise in all of this.

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I guess when the water system isn't being used, the pressure increases to over 100,

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you have just inforned us that you have a faulty PRV valve, Bob's bang on! Replace it and then get back to us. As Bob pointed out the average house pressure runs about 45 PSI. What he didn't touch on was all the bad things that can happen to your system if you allow this high PSI to continue. Excessive water pressure puts a strain on your entire system. Your faucets, the joints, especially the elbos, the ballcocks in your toilets etc. The very first thing you must do is get your house pressure back down to normal. Replace the PRV valve and we will go from there. Regards, Tom