Heating Help

domestic hot water too hot

Homeowner here with a Buderus Logimax GB 142-45 unit with a Buderus
S-120 hot water tank connected. System has "outside" control so
regulates itself depending on outside temperature.

Heating set on auto, hot water set on 120. However when weather gets
cold domestic hot water temperature over rides setting and becomes very
hot.

What to do/ check?

Check flow valve/checkvalve

Easy check is there a flow valve on line that circulates hot water from boiler to tank?  Or does the circulator have a checkvalve/flow check installed?  A good way to check is check temperature of hot water with heat off for a couple of hours.  Then turn heat on, if the hot water gets hotter with heat on, the flow valve or check valve is bad or missing.  Hope this helps. 

domestic hot water too hot

Thanks for this reply. I just found it, I thought the emails were forwarded on automatically, new to system. No, there is no check valve on line and I don't think circulator pump has one in it. How would i tell latter?
This is what Buderus suggested might be the problem. Its a newish system so disappointed contractor missed this bit not totally surprised.
thanks again and i will pursue this line of inquiry

flow check circulator

Taco circulators will usually be a 007, 009, etc...  followed by IFC on electrical cover plate.  Other citculators usually have stickers in box that should have been put on body of circulator.  So, if nothing says IFC or check valve installed, I would be willing to bet its just a regular circulator.  Really easy fix is just have them install one with a checkvalve, IFC (internal flow check) and see what happens.  Or if your pretty handy and they installed it with a shut off valve on each side of the circulator (why doesnt everyone do this?).  Just go to a plumbing supply and pick one up.  I use the taco 007 ifc, or Grundfoss equivalent with flow check.  They are about 75-90 bucks.  Pretty sure this is your problem.  If your friendly to the contractor and insist he try this, most will accomodate.  its shouldnt be more than a 15 minute job. 

domestic hot water too hot

Thanks for your suggestions and going to take a look tomorrow. Your suggestion of just putting in a new circulator with built in regulator might be the way to go as we can't identify the pecks they used to supply and return hot water etc but the circulator we can get out as its copper either side etc .
Thanks again.

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