My T&P valve is expelling 1 cup of water per day

[GrandPooba]

I have a 10-year-old 40 gallon Kenmore natural gas fired water heater that expels about 1 cup of water per day out of the T&P valve. I have turned down the water temperature quite a bit, which doesn't seem to have any effect.

The expansion tank is installed on the hot water line (was like that when I moved in... not sure if this is correct?). It usually expels the water a short time after I take a shower or run the washing machine.

Any thoughts? Worn out T&P valve or expansion tank failure?

 

[Reach4]

You should get a pressure gauge. You will find that when the water is dripping out, the water pressure is over 100 PSI.

Classic symptoms. Probably the thermal expansion tank has failed. You could try putting air in, but most probably it is not worth messing with.


The new one should be precharged with the air pressure that your water pressure is, or a little more.

 

[Sponsor]

 

[Jadnashua]

ET's fail, they fail faster on the hot water side (many are not designed for the heat, some are, but even then, they don't last as long on the hot side as they do on the cold side). Classic symptom of a failed ET.

 

[GrandPooba]

thanks. That sounds like it.

I tapped on my expansion tank and it makes a solid thunk. Correct me if I'm wrong but a working tank should sound hollow right?

 

[Reach4]

Correct. Normally empty.

Consider Therm-X-Trol for the replacement. http://www.amtrol.com/media/documents/thermxtrol/MC4090_01_16_ThermXtrol_Brochure.pdf

 

[Jadnashua]

Be careful when you unscrew it...it will be heavy! If you precharge it properly to your static house pressure (they come typically precharged to 40psi), that will put the bladder at its 'neutral' point, and maximize it's life and function. Since the air volume isn't huge, be careful if you use a compressor...a bike tire pump works.

 

[SteveW]

You can test it by pushing on the air valve (looks like the valve on a car tire). If water comes out, you have a failed tank.

By the way, it normally is about half-filled with water (i.e. the half of the tank on the water input side). The other half should sound hollow when you thump on it, but the half below the diaphragm will always sound "solid."

 

[Reach4]

By the way, it normally is about half-filled with water (i.e. the half of the tank on the water input side). The other half should sound hollow when you thump on it, but the half below the diaphragm will always sound "solid."

Ideally the tank will be empty when you are dribbling a little water from a faucet. An empty tank will give it more space to let the water expand into once you stop using water.

If your tank is half full of water when dribbling water from a faucet, you want to increase the precharge. Record the water pressure while dribbling. Then drop the water pressure to zero, and set the air pressure to that recorded pressure or a bit more.

 

[GrandPooba]

I also need to pick up a pressure gauge so that I can properly equalize the ET pressure. Where should I measure the water pressure from? My water main to the city does not have a pressure gauge built in.

 

[Reach4]

Where should I measure the water pressure from? My water main to the city does not have a pressure gauge built in.

Laundry sink, outside hose spigot, washing machine tap, drain on WH are places that work.

 

[Jadnashua]

You can also pick up an adapter, unscrew an aerator on one of your faucets, and screw a pressure gauge on there to the adapter, but it's easier to just attach it where there's already a hose bib.

 

[Gary Swart]

I cut a tee into my supply line just after the PRV and installed a pressure gauge. Cheap and always right there. I set my PRV at 50 PSI and expansion tank at 45. I use my large air compressor with extreme caution and had no problems. Just remember it's a small volume tank so not much air required.

 

[GrandPooba]

I charged and installed the new expansion tank today. You guys were correct, the old one was completely full of water. Also replaced the old T&P valve, which was covered in crud.

Only bad part was I could not replace the drain valve. The original is plastic and I had wanted to replace with a brass ball valve. It is stuck on so hard and the plastic body cannot seem to handle any torque from my wrench. I didn't want to deform it, so I guess I will ask a pro to do that the next time they are here.

 

[Reach4]

Good work. Sorry to hear about the drain valve.

What does the valve have for a wrench to grab onto? Sometimes a different kind of wrench can grab better.

 

[GrandPooba]

The valve has the typical wrench flats on the side of the body. I tried adjustable and spanner wrench, and a set of vice grips. Would not budge, and did not want to deform the plastic body too much.

 

[Terry]

The valve has the typical wrench flats on the side of the body. I tried adjustable and spanner wrench, and a set of vice grips. Would not budge, and did not want to deform the plastic body too much.

When I remove a plastic drain, I make sure I have a replacement on hand. Sometimes they snap at the tank, and then I need to use a saw blade to make some cuts on the inside to allow me to remove it.

 

[Master Plumber Mark]

I charged and installed the new expansion tank today. You guys were correct, the old one was completely full of water. Also replaced the old T&P valve, which was covered in crud.

Only bad part was I could not replace the drain valve. The original is plastic and I had wanted to replace with a brass ball valve. It is stuck on so hard and the plastic body cannot seem to handle any torque from my wrench. I didn't want to deform it, so I guess I will ask a pro to do that the next time they are here.

this can get real ugly fast...
I have tried to change them out before and had to chisel the old nipple and
pieces of plastic out of the threaded hole ....only to find that after getting the hole cleaned out
that the old threads would not accept my new brass valve that I had all greased up and ready to go..

I had water pouring out on me and I had to run and get a 3/4 tap and re-thread the socket .

be sure you have a 3/4 tap on hand just in case the
water heater wants to fight you to the bitter end...

 

[Jadnashua]

If you buy a new WH, and it has a plastic valve, replace it prior to installation with a solid brass one before the old threads get corroded and the thing gets locked in. Those sold at a plumbing supply house tend to have brass valves...those at the big box stores do not, at least on the least expensive ones.