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Bosch Combi New Install Issues

gitarman
gitarman Member Posts: 7
in THE MAIN WALL
New construction Bosch Greenstar Combi boiler. Radiant heat in slab. Cold nights can't keep up with thermostat, usually 4-6 degress below in early AM. DHW starts hot then goes warm in seconds even though burner is on; temp drops on display. Would just like some tips on possible causes to speak with installer so I can get this resolved quickly. Thanks.

Comments

  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    Has the outdoor reset feature been installed, and properly set up? Are you setting back the temperature at certain times during the day?
    Is there enough radiation installed in the house?
    Has the incoming gas supply been checked for adequacy?—NBC
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,470
    I am assuming you not doing any night setback with the radiant?

    How long ago was the initial start-up ? I am assuming the slab has had plenty of time to heat up. Anything on the floors that is stopping the heat?

    Have the tech check the boiler especially the gas pressure. Check the venting and air intake for restriction.

    Did someone doan accurate heat loss of the house ....or just guess
    SuperTech
  • gitarman
    gitarman Member Posts: 7
    Thanks for the replies. The thermostat is set at 70 and no changes. The only thing on the slab is laminate and tile flooring. I will ask these questions from the installer. Would these questions relate to the lack of domestic hot water as well?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,470
    Yes. If your having issues maintaining boiler temp. You could try shutting the heat down and see if it maintains domestic water.
  • gitarman
    gitarman Member Posts: 7
    Diverter valve on the hot water sides being replaced.
    Would lack of slab edge insulation cause enough heat loss to cause the radiant heat lag? Just strange that if set at 62 (earlier this season) it is at 59 in the AM and now set at 70 is 66 in the AM.
    Thanks again for the information.
  • DZoro
    DZoro Member Posts: 1,048
    Lack of insulation certainly is not doing you any favors. What size home, and boiler? Can you post some pictures of the installation?
    What thermostat do you have?
    D
  • gitarman
    gitarman Member Posts: 7
    Home is small, 825sq ft, with second floor. Well insulated except the slab edge, it is insulated underneath slab. Boiler is Bosch Greenstar Combi 100p natural gas. Thermostat Honeywell non-programmable pro100 I think. I might be able to get there tomorrow for pics.
  • psb75
    psb75 Member Posts: 904
    Your figure of 825 sqft is unclear. Is that the footprint (one floor) of the house or total sqft-age (two floors)?
    It also depends on the size and length of tubing in the slab. If you don't know length, you can use an infrared thermometer gun to locate the runs of tubing--when the boiler is attempting to add heat to the slab. Even easier would be to take a picture with an infrared camera on an IPhone.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,470
    If your not their to keep an eye on it I would put an hour meter on the boiler. This would tell you how many hours in a day the boiler if firing. Also chek the water temp out and back to the radiant and the boiler temp
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,470
    The boiler is 89k out put should be plenty large enough so something is going on
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    On the second floor, what sort of radiation is installed-radiant tubing as well?—NBC
  • gitarman
    gitarman Member Posts: 7
    Thanks everyone for all the thoughts. The DHW issue is resolved. I am having a Bosch Certified Tech come out and verify the heat installation. I’ll post any findings here when I hear back.
  • kcopp
    kcopp Member Posts: 4,472
    What happened? How was it resolved?
  • mikeg2015
    mikeg2015 Member Posts: 1,194
    Edge insulation can be substantial. If this is a tube in concrete slab, could lose 30% of your heat. We’ve seen horror stories.
  • gitarman
    gitarman Member Posts: 7
    The tech said the boiler temp was set too low, about 110 degrees. He set it to 122 degrees. We will know in a couple days, some cold nights still coming our way. Does anyone know if a laminate floor underlayment r-value of .5 is too high for radiant floor? I just stumbled on this trying to find any other causes. I think even 6 mil poly vapor barrier is around this but any input appreciated.
  • DZoro
    DZoro Member Posts: 1,048
    Hope the 122* works for you. Is there any way to add the edge insulation? Are you running outdoor reset control?
    D
  • gitarman
    gitarman Member Posts: 7
    The only way to add edge insulation would be on the exterior foundation walls above and below grade which we will consider. The boiler does not support an outdoor reset.
  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,578
    I see a "weather dependent control listed as an option.--NBC

    https://www.bosch-climate.us/products-bosch-thermotechnology/boilers/residential-boilers/greenstar-gas-condensing-boilers/greenstar-boiler-controls-accessories/greenstar-boiler-controls.html

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