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Buderus is SLOW to react

Tom_133 Member Posts: 864
Hey fellow Wallies,

So two years ago I installed a 4 section Buderus G115, hydrolevel aqua stat with a SSU60 tank, piped the side arm with 1" copper and a 007e. The boiler is piped direct no primary secondary, (won't do that again). I have a Caleffi mixing valve and the tank is set for 140, going out to the house at 120, I believe its just a honeywell aqua stat on the tank, standard on/off

All winter this thing is a champ, it heats water for 8 people, and this big 4500 sqft place in stowe vt

Last summer this thing acted up it was running out of hot water in the summer. I went there and they are saying after a 10 min shower, a second person only gets 5 mins then its cold.

I went downstairs and watched it, and they are correct. The boiler fires up cold and sucks all the heat out of the indirect when it first fires. The boiler can not come up fast enough to not let that happen. I turn the LO temp up to 140 and think ok, well that worked for awhile. Now its back, its still at 140 lo temp, 185 hi temp ( for test purposes). What I am finding is the aqua stat location on the G115 is on top, the rest of the boiler is cooling off down around 120 but the top is still over 140. So when there is a call for hot water, same deal happens it cools the tank with the colder boiler water before the boiler can catch up.

I am thinking of wiring the water heater pump through the circ call on a triple stat to not allow the pump to come on until the boiler is hot but I dont think its going to work the way I want it to, due to the heat all sitting at the top of the boiler. Maybe a delay on the DHW pump so the boiler can get up to temp??

Any thoughts?


Montpelier Vt


    EBEBRATT-Ed Member Posts: 14,505
    I am surprised buderus does not come with controls to accomplish this, I can see this happening with a long time between dhw calls.

    With tankless heaters we would use a reverse acting aqaustat to shut the pumps off until the boiler caught up. You could do that but I would be concerned about cold water coming back to the boiler.

    Best bet might be to adjust the controls to maintain 140 in the boiler
  • Tinman
    Tinman Member Posts: 2,806
    Do you have DHW priority?
    Steve Minnich
    HVACNUT Member Posts: 5,469
    edited June 2019
    Everyone hates the R2107 but...
    What's the differential on the water heater thermostat?
    Which burner and is it firing at .90 GPH?
    If using a zone board is ZR in the Hydrostat wired in parallel to the hot for the indirect circulator?
    Eco mode off if not wired as above?
    The 3250 Plus does offer circulator hold without the need make it triple acting.
    All that aside, the SSU 60 wants 174K input and the G115-4 has 109K gross out. So there's that, unfortunate as it is.
    Try maintaining indirect at 160° with no more than a 10° diff. Might need 5 in this case.
  • Tom_133
    Tom_133 Member Posts: 864
    edited June 2019
    As I mentioned the Lo setting is at 140 and due to the location of the aquastat it doesn't help.

    Yup DHW priority is on

    Aquastat on the water heater is a cheap on/off, no differential so whatever is put in by honeywell. I guess I need to know that answer. The ECO mode is off, I will look at the wiring on the current hydro level and see what it offers. I will look for an aqua stat that can be raised to 160 and has a settable differential.

    Montpelier Vt
  • DZoro
    DZoro Member Posts: 1,048
    You mentioned it is piped with a 1" side arm. Is the side arm similar to a outdoor wood furnace side arm? How many btu is it rated for? Do you have a picture of the installation?
    Is there any chance that the cold water is entering the tank and going directly into the side arm and out the top, then into or next to the hot supply out. Thus making a easy route for the incoming cold water to enter and exit the side arm too fast, and the side arm is not sized to be a on demand H/E and can't instantly heat that water to 120*.