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  1. #1
    Join Date
    Aug 2008
    Posts
    5

    Default On demand water heaters

    We have a Bosch gas on demand water heater. In the summer time (mostly) I can't get warm water in the shower in the master bath. When I turn the lever to the cooler side to cool down the hot water, I have warm water for about a minute, then it gets hot again and stays that way until I turn it so far to the cooler side the heater is no longer heating the water. How do I get warm water? I don't have a problem with the kitchen faucet and it is also a single lever faucet. Any help you can give would be appreciated. dpmath (Dan)

  2. #2
    Join Date
    Dec 2007
    Location
    MN
    Posts
    455

    Default Re: On demand water heaters

    Seems to me I read somewhere here that unbalanced water pressure or a temperature balance mixing valve at the shower can be a cause.

  3. #3
    Join Date
    Feb 2008
    Location
    Nashville, TN
    Posts
    149

    Default Re: On demand water heaters

    I agree about the mixing valve of the shower that might be the problem. However, you may also have a crossed line somewhere and the hot water is bieng mix with the cold side unintentionally. Trace the lines to make sure cold is cold and hot is hot.
    Process of elimination. Good luck.

  4. #4
    Join Date
    Aug 2008
    Posts
    5

    Default Re: On demand water heaters

    Thank you for the replies. I'll have the mixing valve checked as I know the water lines are ok.

  5. #5
    Join Date
    Feb 2008
    Location
    Nashville, TN
    Posts
    149

    Default Re: On demand water heaters

    I am still curious as to why the master bath shower gets the either cold water or the hot water and not the mixed warm water. it has got to be the shower valve itself. as you run the water thru the pipes, each pipe respectively, you should be able to feel its temp. And like you checked, the cold is cold and the hot is hot. It has then got to be the shower valvel.

    I know when i have soldered on my copper conection, i have taken out the cartridge so not to heat it up as well. if they aren't put back in the right way (espically with Moen) then the water temps are flipped.
    Process of elimination. Good luck.

  6. #6
    Join Date
    Feb 2008
    Location
    Memphis, not Egypt
    Posts
    183

    Default Re: On demand water heaters

    I think fitter has a good point Delta is the same way too. If the cartrige is upside down it won't make any sense and the scald guard makes it worse if there is trash in the pressure balancing ( if equiped ) portion of the valve. You'll know if its wrong cause it will be hot first instead of cold.
    Last edited by i.m.plummin; 08-11-2008 at 08:05 PM. Reason: more information

  7. #7
    Join Date
    Aug 2008
    Posts
    5

    Default Re: On demand water heaters

    Thank you both for your suggestions. We turned down the hot side of the mixer valve and that didn't work either. It's almost as if the heater is shutting down the cold water to maintain the set water temp (116). May be time to call the plumber that installed the heater and see what he can find. I know one thing, if I put in another on-demand heater, I'll be sure there are separate handles for the hot and cold water in the shower, like at most bathroom sinks/tubs.
    Last edited by dpmath; 08-19-2008 at 11:38 AM.

  8. #8
    Join Date
    Oct 2008
    Posts
    3

    Post Re: On demand water heaters

    Pressure balancing and on-demand systems don't always get along. What kind of shower valve do you have?

    More than likely the on-demand system can't keep up with the amount of water being demanded by the shower, so it slows the flow of hot water to maintain the desired temperature. Go with a thermostatic valve instead of a pressure balanced one next time! Both pressure balanced valves and thermostatic valves are the same in that they both prevent "Shower Shock" (you know that lovely blast of hot water you used to get when your little sister was mad at you and decided to flush the toilet while you were in the shower). The difference though, is that pressure balanced valves do not in any way, shape or form recognize temperature - they will only put out the water that is coming to the valve. A thermostatic valve on the other hand uses a wax pill inside the cartridge assembly to recognize and maintain a certain temperature of water.

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