22rifle

What? The tankless does not heat water? Gimme my money back!

Kidding man! I know exactly what you meant. Just had to razz you a bit.

Seriously, I am not talking about the OP's case. I am talking in general here. Trying to understand where Ron is coming from.

smellslike$tome

??? Out the t&p valve. Does no one but me experience this with a regular tanked water heater?

If I were unscrupulous I could sell probably 2 water heater installs each week because people call in a panic because water is leaking out onto their floor from the water heater. The leak point is nearly always the t&p and is the direct result of either high pressure (failed prv) and/or thermal expansion (failed or non-existant exp. tank). Now the ho doesn't know the difference and it would be easy enough to sell them a new wh, exp. tank, and prv except for the fact that it would almost always be unnecessary to replace the wh under these circumstances. It is however necessary to replace the prv if it is bad and to install an expansion tank if there is none or it has failed.

Think about how many houses you go to in which the relief line goes through the floor or out a wall. These people have no idea they are even losing any water at all. They are paying to heat water only to have it discharged through the relief line because of thermal expansion. Oh yeah and t&p's don't always open when they are supposed too either. I have seen them go as high as 165 psi before opening. The t&p almost always is just doing it's job though and doing it correctly. Very rarely will I find a t&p that is bad and when I do it is nearly always some physical damage.

It has just become automatic with me to perform this test and have this discussion with the ho in every house I go into. Once I have explained everything and shown them that they have high pressure and if they then don't want to do anything about it, fine, that's up to them but I am going to make certain that they understand that they are throwing water and energy away and wearing out their fixtures prematurely.

Now, back to the tankless. Looking back on it, and being of the opinion that a working prv should never be touched after about a year or two, not even for adjustment, I'm betting that it has failed and when I test it in the morning I will find just that. If thermal expansion was a problem with a tankless system then I would expect that they would have very clear references and warnings contained in the install instructions. I have not found any mention of it for Noritz and don't remember any reference to it for Rinnai or Takagi. Believe me I would not miss an opportunity for add on sale of an expansion tank if I had any idea that it would be necessary.

I will find out in a few hours.

Ron

The relief valves on the heater are the required 150psi, the pressure created during the heating phases on a tanked heater is not great enough to exceed the 150, if it don't exceed, the system will handle the expansion, I don't know the science behind how much pressure will build under heated water in a closed system, but it might have some thing to do with developed length within the system, the shorter the developed length the less capacity for water to pressurize in it, if the DL is short then an expansion tank could be needed. I'm just talking off the top of my head on what I think is taking place inside the closed system. It may all seem crazy to you that here we hardly install expansion tanks, but believe me, it's not being done here.

It's just not a big issue in residental homes here.

__________________
Stephen Hawking: If the government is covering up knowledge of Aliens, they are doing a better job of it then they do at anything else.

smellslike$tome

This is the response I was looking for! Thank you. 40 installs with no expansion tanks is enough to satisfy me.

22rifle

Thanks Ron. I respectfully disagree with you when you seem to say it's OK as long as it doesn't go over 150 psi. I don't want to see it going over 80 psi. like the UPC requires.

Do this sometime. On a system you know has no leaks, put a pressure gauge on a gas water heater and turn the gas up enough to kick it on. I think you will be amazed.

I forget, do you use copper or PEX?

22rifle

Yeah, we all got off onto tank systems. Sorry about that man.

A tankless never heats any significant amount of water unless the water is flowing which automatically relieves the pressure.

Ron

Pex always.

That's fine if you disagree with me, was not trying to make you agree with me, I'm just letting you know what it is we do here.

__________________
Stephen Hawking: If the government is covering up knowledge of Aliens, they are doing a better job of it then they do at anything else.

22rifle

Sure. It's cool. I wasn't trying to do anything but understand you.

I wonder how much PEX gives as opposed to copper.

Alan

We always do because code requires it, and actually have solved a myriad of leaky t&p valves with expansion tanks.

smellslike$tome

PRV is the winner but still not without one more thumb in my eye. Ran the test and it's definately the prv so I crawl under the house and change it out. Crawl back out and check the pressure, ... 100 psi! Oh man! What have I missed? So I'm standing there scratching my head and finally decide well it must be a bad prv right out of the box. So I grab another one off the truck and back under I go. Changed it out again (love doing stuff twice especially when there is a cs involved), crawl back out, recheck pressure, 55 psi . I could probably sink a destroyer with all the prvs I've changed out (well maybe a canoe) but this is the first time I've ever had one bad right out of the box.

Anyway, mystery solved and I have concluded, until shown otherwise, that an expansion tank is not necessary for a tankless water heater.