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2 buderus g115 with logmatic and 16 zones

acaciolo Member Posts: 12
Hello Everyone!

Total newbie here looking for a little advice.    I am a custom home builder in PA and I have a fairly complicated buderus set up in my personal home that is giving me some headaches....and my local service techs aren't too great with buderus.

The system consists of 2 G115's with a 2017 logmatic control with the dual burner module installed.     There are about 6 non mixed hot water baseboard zones and about 10 mixed radiant floor zones.  They radiant zones are controlled by a taco injector pump (can't remember the model number) but it has temp sensors strapped to the radiant side to control the amount of hot water injected.

There also is a 110 gall buderus domestic hot water tank (and we were, but aren't anymore, using a 350kbtu heat exchanger to heat the pool...but that has been removed.)

All thermostats are tied into an automation system so we have full temperature setback control in each room from the automation system.   I am not using logmatic for anytype of temp setback.

I've been having some problems with the high temp reset blowing...so my heating contractor did something (not sure what yet) and changed out a honeywell aquastat (not sure why that was on anyway) and now the pipe temp is getting to 230!    They will be out on monday to correct their miswiring problem.

Anyway..my little boiler room is always crazy hot (luckily we have fresh air intakes)..and I am tired of the boilers keeping warm all year round.   My hvac contractor wants to change them to cold start, which I think I want to do also, but I am not sure if there is anyway to do that with logmatic (I don't think so) and then I also have the problem of controling my DHW and the 2 boilers.    The 2nd boiler only comes on now if the main boiler can't keep up (which is rare) or on a dhw call.

We are using taco controls for the baseboard and radiant circulators, and there is a system pump also.

Question is, since I'd like to do cold start, is there an easy way (with or without logmatic) to do this and still control dhw and the dual boilers?

thanks in advance..and sorry for the rambling.

tony c


  • Alan R. Mercurio_3
    Alan R. Mercurio_3 Member Posts: 1,620
    RE: Buderus

    It sounds like you may have controls that are not able to communicate with one another. Also even with the logamatic the boilers should be operating in a cold start mode.

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  • Ironman
    Ironman Member Posts: 7,379
    Logamatic Control

    The 2107 Logamatic operates off of its reset curve and its WWSD setting. It does not operate from a demend signal per se. Therefore, it's not designed for cold start. If your boilers are staying warm (or hot) year round, then the control is not setup correctly. That's excluding a call for DHW.

    The system will operate far more efficiently and burn much cleaner with the Logamatic setup properly than it would if converted to cold start. You need to find someone who knows how to properly setup the control.

    Where are you located in PA?
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • acaciolo
    acaciolo Member Posts: 12


    the outdoor temp sensor failed and was reading -39 degrees, so the logmatic was running the boilers at max temp.   at the same time, the honeywell auqastat high limit failed and was allowing the boiler to overheat.  so both of those problems are fixed.

    Regarding logmatic vs. a true cold start.    with 11 zones of heat, I can't really use, nor does it make sense, do do a constant circulation.   So as it is wired now, the logamatic keeps the boiler to a temp based on the outdoor temp.

    but even in the summer, when we have 0 demand, the boiler room is hot all day and the temp stays at 110+ (based on the outdoor temp.)         I don't know if WWSD should allow the boiler to cool down completely, but it doesnt' seem to do that.     Keep in mind, we have our dhw through this.

    it seemed (maybe incorrectly) that in the summer time and fringe months when we aren't using heat, I should let the boiler cool off since the buderus is ok with cold start.  and then fire up on a dhw call.   thoughts on that?

    I am in the allentown pa area.


  • STEVEusaPA
    STEVEusaPA Member Posts: 6,505
    Hello Allentown....

    I'm down here outside philly.  I do agree with Ironman about cold start.  You do have quite a large system, and a large storage tank for DHW.  That being said, depending on how many people are in your house all day, using hot water, the boilers are just doing their job.  Even set up for cold start (not my cup of tea), the boilers would maintain a warmer temp between off cycles for a DHW call.  A working example from my house, 2 adults no kids, summertime.  My wife showers 6am, boiler fires for DHW (usually gets up to 170).  I get home 7-8 pm, the boiler didnt fire all day, temp is about 90-110 degrees.  I shower, boiler fires for DHW, runs up to about 170.  Doesnt fire all night.  Your boiler(s) are probably staying warm just because they have to fire 3-4 times a day.  So if you had your problems fixed (sensor, aquastat fixed), I would just leave it as is.

    As far as non communicating controls, are you having short cycle issues?  This is where the communicating controls, and t-stats would help.  The boiler fires when it's told to (temperature), and doesnt know in 30 seconds, or a minute, etc., that the call for heat would end.  Communicating controls, would delay firing (sometimes not fire at all), or bring up a zone thats about to call for heat, and things of this nature, to help smooth out the run times.  But with all thoses zones, im sure in the winter, there's always a few zones calling.

    On the coldest days, are both boilers firing almost continuously?  If theyre not, then maybe their oversized and you could make some control adjustments to compensate, like lowering the reset curves, water temps, etc.

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