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Thread: Help on On-Demand Hot Water Supply Issues

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  1. #1

    Default Help on On-Demand Hot Water Supply Issues

    Hi, and thanks for helping.

    I have a home with an oil fired steam furnace that was installed in 2003. At that time I also had the oil company install a tankless water heater system.

    At the current moment I am having problems maintaining a desireable temperature when taking a shower. Here are some details (please let me know if I should capture others):

    Maintenance Temp of Boiler: 180
    Water Pressure: 75psi
    Water Supply Pipe Diameter: 3/4"
    Hot Water Outlet Diameter: 1/2"
    Temp at kitchen Sink Faucet: 120 - 130
    Temp at bath sink faucet: 119-124
    Temp of Shower: 105-114
    Shower Valve Type: Single Handle Symmons
    Anti-Scald Stop Setting: Open

    Basically the issue is that the hot water coming out of the sinks is almost too hot and I am worried about accidental scalding. However, if I adjust the boiler to where the max faucet temp is 115, the shower temp is horrible. The shower valve is brand new and was just replaced. The stop screw is set so that the water handle can be turned to the fully open hot position.

    I am stumped as to what is causing this and how I can rectify this. I would like to have the faucet temp be around 115 to 120 and the shower between 125 and 130.

    I have had the oil company back out to check their mixing valve and they say all is well. They point to the anti-scald valve, but my plumber says it is not that.

    Any advise would be appreciated and if I need to collect any other details to help please let me know.

    - vince

  2. #2
    Plumber patrick88's Avatar
    Join Date
    Sep 2007
    Webster Ma.


    That is some big temp drops that you seem to have.
    Is your house very large?
    Is the shower more than 100' from the water heater?
    You could install tempering valves at your other fixtures.
    Did the plumber pull the spindle out (stem) and check it.
    Do you have well or city water?
    How cold is your cold water?

    Sorry to jump around with the questions, but sometimes different things cause the same problem.
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

  3. #3


    Hi Patrick,

    Thanks for responding.

    Is your house very large?
    I have half of a duplex, and my oil company tells me that the furnace is more than adequately sized.

    Is the shower more than 100' from the water heater?
    The boiler is in the basement and the shower on the 2nd floor. Its probably 40'-50'.

    You could install tempering valves at your other fixtures.
    Thanks, I will check with my plumber on this.

    Did the plumber pull the spindle out (stem) and check it.
    As part of this whole troubleshooting process we actually replaced all symmons valve components. New hot and cold seat, new spindle, and new cap. The set screw is all the way out so the cap can sit flush against the top of the spindle (and thus open all the way in the hot position).

    Do you have well or city water?
    It is town water which is supplied by MWRA (treated reservoir water)

    How cold is your cold water?
    I will recheck and post, but last time I looked it was about 50.

    Thanks again,
    - Vince

  4. #4
    Retired Defense Industry Engineer jadnashua's Avatar
    Join Date
    Sep 2004
    New England


    Check the flow rate...take a bucket and a watch. My guess is that on the shower, you're pulling more water in the same time than when you are at a sink. The thing can't keep up...it's like you put the pot on the stove, but trying to heat a cup of water verses a quart, in the time you have as it passes by the heater, the cup will get much hotter than the quart will.

    It may not get any better. You notice it more in the winter because the incoming water is much colder than in the summer. I gave up and put in an indirect WH at my place. A quality indirect is very well insulated, and the best ones only lose maybe 1/4-degree per hour, so may never need to run except to replace the water drawn. On an indirect or electric WH, there just isn't a lot of waste in standby losses, contrary to what the tankless people tell you. A flame heated WH isn't as efficient since you have to have that flue and heat exchanger that is uninsulated.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014


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