For starters my home is about a year old. The other day I added a thermal expansion tank because the pressure relief valve popped off causing water to drain from the hot water tank. I followed the instructions:
1. Checked the themal expansions tank pressue to insure it was 40 pounds.
2. Install the thermal tank
3. Drain the hot water tank so water was below the pressure relief valve. Open the pressure relief valve.

Next I opened all of the facwetts (inside and out) and flused the commodes. Then I opened the main water. After the water started to flow, I shut the vales off staring at the lowest point.

I left a hot water facett drip until the hot water tank quit heating.

I no longer have a promlem with the pressure. It stays around 58 pounds.

BUT NOW I GET A SINGING NOISE A FEW SECONDS AFTER A FACWETT IS SHUT OFF OR COMMODE SHUTS OFF.

The noise appears to come from the main shut off area, but, I cannot be sure.

Any suggestions on how to identify the problem area or possible solutions.

Regis

I think your 58 psi is still a bit high. I shot for 45 psi, 58 can be just enough to push water past a washer and that's your noise. The expansion tank is great if your problem is caused by expanding water causing increased pressure. You may just have too much pressure entering the house. I'd install a pressure reducing valve by the main shut off. Also consider that T&P on the water heater should not have popped until it read 210 degrees or 150 psi. Anything short of that is likely a bad T&P valve and should be replaced.

Ballengerb1

The water pressure has always been 58. It would periodically go higher and the T&P would leak a small amount of water. Last week it popped off. This was the one and only time water poured out the T&P. There is a pressure reducing valve on the line.

Since I put the tank on the pressure has stayed below 60 pounds.

The

One point that Ballengerb1 made, but didn't elaborate. Your temp may be too high. Check to see that your thermostats are set to 120 degrees. It will save you energy, and help avoid over-pressure blow-off. You can verify that they are correct with a thermometer in the hot water stream. Even if they are set properly, they may be malfunctioning.
Al

I checked the water temperature before I started this process and it was 120 degrees.

The pressure and temperature both seem to fall in an acceptable range.

Take a towel and wrap it around the pipes, then the pressure relief valve. See if you can isolate where the sound is coming from.

When you say that you checked the temp, do you mean with a thermometer, or you checked the thermostats on the heater to make sure they were set correctly?

I measured the temperature with a thermometer.

I will try you suggestion. I do not know what else to try.

Thanks

Regis

Let me repeat myself in different words. A T&P will pop under more than 210 degrees, more than 150 psi or if its defective. Those are the three reason, period. If your T&P popped you had at least one issue present. You installed an expansion tank thinking this was a pressure problem caused by the water heater expanding the volume of the water. However, a tank will not cure the other two problems, you have at least one of those problems. That singing is excessive pressure forcing water through a washer in a valve that is trying to close but the pressure is higher than the valve will accept. 58psi is not the worst I've seen but it is 25% higher than any plumber will say you should have. A pressure reducing valve (PRT) will cure that issue. There is also the chance that once a T&P opens they will not always close completely because some heater tank debris got hung up on the seal.

I am trying to understand the situation. I undersatnd what you wrote in your latest reply.

As I noted earlier, I have a pressure reducing valve on the system. Can I test PRValve to see if it is working correctly?

If the pressure has always been too high at least 58 pounds or higher, why haven't I heard the singing noise prior to my adding the thermal expansion tank? It seems too much of coincidence that this problem occurred after I added the tank.

Have you ever measured the pressure prior to the PRV? If it comes in 58psi and leaves 58 the valve isn't doing anything but they are adjustable. Usually they have a nut with a set screw or bolt. Loosen the nut, tighten the bolt and then tighten the nut. Test your pressure again, it should have gone dow, or up if I'm backwrads with my bolt info.

I reduced the pressure at thePRV to 45 pounds and the pipes still sing

Do you have a check valve on the cold water line to the water heater. Some PRV's have by pass that releases pressure back to the main if the pressure on the house side exceeds the main pressure by 10 lbs. The installation of the expansion tank may have created that condition. Do you get the singing if you slowly close a faucet?

What is a check valve? Where would it be located? It does sing after I close the valve SLOWLY. Yesterday, I drained the water line and the hot water tank below the pressure relief valve. I turne the water back on and ran the water for 5 mintues. There was no singing for about 5 hours. The singing slowly came back.

A check valve is a valve that allows water to only flow one way. Put it in on the cold water input line to the water heater.

Where should the check valve be installed ?

1. Between the hot water tank and the thermal expansion tank?

2 On the cold water line right before the thermal expansion tank

3 Near the water meter and the PRValve.

Can I check anything to ensure I need the check valve? I was gong to cal the water company and have them check out the water meter. As you ar aware , they can put in a by- pass pipe.

PS

I just found a check valve ASSE 1024 right after the meter on the house side. Could this be mal functiong and causing the problem. If I put my ear on the pipe I hear a chatter noise before the singing starts.

On the water line before the thermal expansion tank. I think expansion tank is causing the pressure differential which is causing th pressure relief in the PRV to kick in. Don't bother checking anything, they are cheap and you just cut the line and solder in. If you don't need it you haven't lost much.

Do I need a check valve inaddition to the one loacted at the meter? If yes, what are the check valve specs.

Right now it appears you need one to prevent pressure from the expansion tank getting back to the PRV valve. Just get one to fit the size pipe, probably 3/4".