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Combi boiler dhw and heat or dhw or heat

XmytruckXmytruck Member Posts: 85

Last night I noticed when my wife was washing the dishes with hot water and the dishwasher was running. I was downstairs the basement and I noticed that the supply temp drop down to hundred and 20° which is what the dwh is set too. I noticed that the pipes for the baseboard he became very cool even though the system was calling for heat. Once she shut off the hot water the supply temp jumped back up to hundred and 60 and the baseboard Became hot again. Is this normal does this systems only can do one task at a time they can't keep the house and generate hot water at the same time? The product is a Navien ch240a.




  • RichRich Member Posts: 2,228

    Your combi can make hot water or heat , but not both at once .  This is so with many new systems even if they are component based . The only way to do both is either have separate water heater and boiler , imagine that or to oversize the equipment so enough BTUs are available to support both operations at once . There are a couple options for this without GROSSLY oversizing but that is not for this thread . Your unit is working properly .  There is a diverting valve within the unit that diverts flow one way or the other .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • JackJack Member Posts: 936
    you can get

    "proportional" priority on some equipment. The boiler will make heat and on a call for hot water will shed some of its capacity to hot water. As the hot water load increases the heating side diminishes until it is all DHW priority.
  • HomeOwner1HomeOwner1 Member Posts: 134
    That is normal on a combi

    We own the same unit. Your hot water will take priority over heat.

    We set our hot water temp to 130, as it compares more to our previous hot water system at that temp.

    Also, we set ours up for the well water setting.

    How has yours been going? How big is the home and how many baths? Our experience has been very positive so far.
  • XmytruckXmytruck Member Posts: 85
    Like it

    So far no major complaints ( Knock on wood) the house is 2200 sq feet and 2.5 baths. Currently we have the DHW set at 120 and the heat to 180 with the unit running on low temp. I am tempted to switch the unit to high temp because when it gets single digits or below zero the system is always running and it hard to maintain the house at 72. Usually on a single digit day the house is at 68 with the temp set to 72. Single pane windows do not help and we use to have oil and we do not have enough base board and when I made the switch I did not note what the temp was set too. The only other issue is during the warmer months that we experience cold water sandwich. But that could be solved by installing the remote or switching the pre-heat switch. I prefer to save on the gas and let the water run a little Annoying sometimes it like half of a bathtub of water.
  • bld999bld999 Member Posts: 43
    Let the mixing valve

    take care of the dhw supply temp and set the dhw control value to 140 or higher. That way your mixing valve will produce stable hot temps. You may quit condensing at that time, but have a happier crew in the house.
  • HomeOwner1HomeOwner1 Member Posts: 134
    Our unit is that way too.

    We set our family's unit to 130. There was a way to get into the special settings to override that to get above 120. Works well at that temp.

    Also, we set ours to the well water setting. Our installer said it works better on that setting for most people.
  • HomeOwner1HomeOwner1 Member Posts: 134
    Mine does not run all the time

    We have close to 4000 sq feet but with good windows. Our unit is using the outdoor temp sensor option to modulate, so it sets the loop temps itself based on need. More efficient that way.

    Even during the -3 degree weather we had recently, our unit never had to work all that hard. I don't even think our loop temps went over 160 and we kept the house at an even 72. It was a good test to see how the unit would do in extreme weather for our home.

    Do you have a picture of how your unit is installed?
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