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Thread: Scalding Hot Water

  1. #1

    Default Scalding Hot Water

    I recently moved to a new house which uses the oil burner to heat hot water (previously I had a gas water heater). The hot water is too hot. I've been told that I can utilize the mixing valve to control the temperature of the water (I've been able to find the valve). I 've also been told that the hot water temperature should be around 120 degrees in order to save fuel. Just wondering if what I've been told is true and what is the best way to test the water temperature. Thanks.
    Last edited by John456; 11-30-2004 at 10:32 AM.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Does the oil burner heat the water in a separate tank? If so, then it should have its own thermostat to control the water temp in that separate tank. If it is sort of a tankless system, then it needs a mixing (tempering) valve to restrict the output water to that temp desired that is safe. Adjust that valve, and you should be okay. If it does not respond, you may need a new valve. If a tank, and the thermostat does not work, then you'd need to replace that. My opinion...
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Senior Member e-plumber's Avatar
    Join Date
    Sep 2004
    New York

    Exclamation Scalding Hot Water

    The best way to test the temperature of the HW is from a faucet, preferably the kitchen sink or utility sink faucet.
    It sounds like there is an internal coil in the heating boiler to produce domestic HW, if you found the tempering valve try to adjust it. If it doesn't take an adjustment, instead of replacing the complete valve, just replace the guts to it, this way you do not need to touch the piping.
    Average, (safe) HW temp is between 110F & 120F.

  4. #4
    Moderator & Master Plumber hj's Avatar
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    Aug 2004
    Cave Creek, Arizona

    Default water

    An interesting footnote, is that an article in PMEngineering stated that a lot of public places, (91%), had water temperatures in excess of 115 degrees, which created a liability hazard. The next paragraph stated that 47% of them had temperatures below 124 degrees which would encourage Legionella growth, which has its own liability. I guess you can't win no matter what you do.

  5. #5


    Thank you for your comments. I did check the temp from the faucet and it registered 167 degrees. I was able to adjust the temp through the mixing valve and brought it down to 115 degrees. I now feel better knowing that there's less chance that my 3 year old will be scalded and I'm saving a little on fuel costs.


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