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Indirect not keeping up

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Miata
Miata Member Posts: 17
I have a 15 year old WM oil fired burner that supplies 2 heating zones and a WM 40 gallon indirect with a zone valve. There is no mixing valve at tank. In November a Roth tank was installed outside. Have had no problem with heat. Every winter while taking a shower the mixing valve on shower control needs to be slightly moved towards hotter to compensate for colder water coming in from the street. So this is normal. My problem - This year while taking shower I need to keep moving control to hotter as time in shower progresse. Today was shaving and washing machine was filling. Almost used nothing but hot water from 2 handle sink to shave. Ran down stairs and furnance is running and pipe into tank is too hot to hold as is return. So I am sure the temp control on tank is working because water is always very hot to start, but appears recovery rate has changed. Expansion tank is hot on top and cool on bottom. I only added information about new Roth tank because it is only variable I am aware of and heating has been just fine. High limit 190 and pressure hot at 25 psi. Boiler fires with no problem when tanks calls for water. Thank you

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  • Jamie Hall
    Jamie Hall Member Posts: 23,324
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    Indirects have a heat exchanger coil inside, and that coil can get scaled up over time, either inside or outside. The tell-tale is that both the inlet and outlet from the boiler are hot -- the inlet should be, but the outlet shouldn't be much warmer than the hot water line coming from the top of the tank.

    Descaling the inside of the coil can be done -- there are various chemicals which you can flush through it (disconnect it from the boiler). Some people even claim vinegar works, though I have my doubts. Descaling the domestic water side is harder...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • Zman
    Zman Member Posts: 7,569
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    Your indirect is a rebadged triangle tube smart tank. It has a tank-in-tank design which gives it tons of surface area and a large volume of boiler water in the outer jacket. Because of that design, those tanks are notorious for overshooting. A thermastatic mixing valve would have been called out in the manual and would be an excellent idea that would solve your problem. I am not sure why someone decided to install an expansion tank in that location but I doubt it is related to the hot water temperature.
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,544
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    Could be a dip tube problem
  • Miata
    Miata Member Posts: 17
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    Could you provide more information about what could go wrong with drip tube?
  • Zman
    Zman Member Posts: 7,569
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    If the dip tube falls off inside the cold inlet of the tank, the water does not mix properly creating inconsistent temps.
    I have found that those tanks need mixing valves or you get slugs of super hot water at the beginning of a shower.

    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • mattmia2
    mattmia2 Member Posts: 9,670
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    The broken dip tube would also explain why the supply and return are hot, most of the tank is still hot but the cold water coming in is going right back out the outlet.
  • Miata
    Miata Member Posts: 17
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    Thank you for your help. Now I have to figure out how to check the dip tube
  • Larry Weingarten
    Larry Weingarten Member Posts: 3,304
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    Hi, The best way to check a dip tube is to pull it out and have a look, for holes, cracks, or part of the tube missing. A far second best is to run water and see if anything high up in the tank cools down too quickly. If it does, this suggests that cold water is not being delivered only to the bottom of the tank.

    Yours, Larry