Water Heaters - Hot Water is constantly draining out from the water heater

Hi all,
I have less than 4 yrs old house and the builder installed two 40 gallon each water tanks ( they were supposed to install 60 gal tank but they realised that the height of 60 gal was too much to fit in - so they oped for two 40 gal tanks).

On the top of the right tank - there is small copper pipecoming out - which goes to the drainage of the heater. This pipe drains hot water constantly. Since the heater is out of the warrenty - the builder wont fix it but they told me that the "Pressure Release Valve" might be bad and needs to be replaced ( this guy told me on phone so I consider this as his assumption). I read in this forum about Pressure Release Valve (PRV) issue but that didnt help much.

I checked that the PRV in my water heater is on the side of the tank and I tried to open/close it as It was suggested in few topics..... but the PSV is connected to some other Plastic pipe - and once I open/clise the PSV, water runs out of that pipe. But the water flow from the copper pipe is still on continuously.

Can anybody throw some light on what could be the problem and HOW that can be fixed.
P.S. : This is my first post to the forum.

Thanks in advance for you help.

Welcome to the forums and take some time to look around at all the stuff...

I read you post a couple of times to make sure I was reading what I was reading. Okay....

If you are describing a brass looking thing with a trip lever on top, that is a T & P valve (temperature and pressure).

This valve only works when you have too high a temperature of 210 degrees or a pressure over 150 PSI.

These valves will also vent after several years of just sitting there and the spring weakens a little bit and the water pressure flucculates some. A person testing this valve can also cause a leak due to some sediment being stuck on the seating face and this not allowing the valve to close.

Now in your case, I would first check the pressure on a convenient hose bib or sink faucet. You can buy a cheap pressure gauge at a big box store. You should buy one with the lazy arm and leave it in place overnight. This will show you how high the pressure climbs and if you have a pressure problem.

Only after I had low pressure confirmed, would I replace the T&P valve for your leaking heater.

You need to look for several things on your water system.

Is there any type of check valve or backflow on the water line coming into the house or on the line going to the water heaters? If yes, you will need to add an expansion tank to the line somewhere very convenient.

Are the heaters ran in series or parallel? Series would be the better choice because parallel requires some decent plumbing skills to install and it is done wrong many times.

What size is the little line you are describing that drains constantly, 1/4" - 1/2" - 3/4" - etc... AND does it just attach to the "thing" and drain off somewhere next to the tank?

More questions or comments, ask away and someone will answer you...Good luck...

If you could post a picture of this setup, it would be helpful.