Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit

Noritz tankless gas water heater

I sold a contractor a Noritz 199,000 BTU input TGWH and he installed it in his showroom as a live fired unit. What happens when the unit is done running and it stops making hot water the relief valve pops off and a little amount of water runs out of  the relief valve. They have high incoming water pressure and I told them to install a PRV unit to reduce pressure. He said no he likes high pressure. Then I suggested to install a small thermal expansion tank. Putting the expansion tank on the cold water inlet pipe to the TGWH would that keep the relief valve from popping? 


  • IronmanIronman Member Posts: 5,514
    That's Exactly...

    What I would have recommended and what inspectors are requiring on all water heaters connected to municipal water in our area.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • bob eckbob eck Member Posts: 908
    Noritz tankless gas water heater

    when contractors in my area put in tank type electric or gas water heaters on public water systems they do install a thermal expansion tank but when they install tankless gas water heaters they do not put in a expansion tank because the only time the unit fires is when water is running through it and a faucet is open. I never was a relief valve on a tankless water leak except on this job where I know they have extremely high water pressure. thanks for the info                
  • IronmanIronman Member Posts: 5,514
    The Issue...

    It isn't the type of heater that causes the problem so much as the high water pressure combined with fast closing valves on clothes and dish washers, etc. Adding water hammer arrestors to these would also help.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • Mark EathertonMark Eatherton Member Posts: 5,843
    There are two sides to every...

    T & P relief valve. Are you sure its not a thermal release instead of a pressure release?

    Residual heat in a combustion chamber can rise up and cause the relief valves thermal sensing unit to see the heat and let some water out.

    Easy enough to figure out. Put a Slow Hand recording pressure gage on it and see what the max pressure you see will be. If it is within reason, the problem is not pressure.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
This discussion has been closed.


It looks like you're new here. If you want to get involved, click one of these buttons!