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buderus boilers

Joe is there any way to limit the dwh hx temp.

I recently added an indirect to a Tekmar equiped gb. Because i was concerned about tripping my radiant high limit after a dhw cycle I set the supply water to the indirect at 165. This temp certianly limits recovery rate but it does not seem to be an issue for this particular user.

Seems like lower than 190 dhw hx temp. would be more efficient, would protect anti-freeze and probably be less hard on the boiler in-terms of thermal stress.

Any means to limit this temp in a non third party control set-up?


  • Karl_4
    Karl_4 Member Posts: 11
    heat exchangers

    Is anybody having issues with using certain types of "aluminum safe" antifreeze? Is anybody having problems when using water only? This is regarding GB boilers.
  • ScottMP
    ScottMP Member Posts: 5,884
    I am having

    no problems with water and I use the approved anti-freeze.

    I have "heard" of others having by Not using the approved product.


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  • Joe@buderus_2
    Joe@buderus_2 Member Posts: 302
    Heat exchangers

    We have seen some issues with some of the "aluminum safe" antifreeze when it is used in temperatures in excess of 180 degrees F. Buderus currently recommends "No-burst-AL" by Noblis or "Rhogard" by Rhomar (if the local distributor does not have access to either of these anti-freeze, they may order from Buderus). On a call for domestic hot water the GB142 series boiler fires up to 194 degrees F. Please contact us if there are any questions.
  • Dave_4
    Dave_4 Member Posts: 1,405

    Joe, Thanks for the mention. Slight correction; it's Noburst AL made by Noble.
  • Paul Fredricks_3
    Paul Fredricks_3 Member Posts: 1,557

    I'm not familiar with the problem. What happens and what are the symptoms?
  • Joe@buderus_2
    Joe@buderus_2 Member Posts: 302
    DHW Call

    There is not a way to set the high limit when the GB142 is in DHW production. On DHW production the GB142 will fire up to 194 degrees F. Thanks for the correction on the anti-freeze name, sorry about the mistake.
  • Dobber
    Dobber Member Posts: 91

    Are you saying that there is an issue with the GB's,that are being used with Glycol,that are also being used with an indirect???


    There was an error rendering this rich post.

  • scott markle_2
    scott markle_2 Member Posts: 611
    My problems

    Paul, the problem for me is that my radiant configuration has no mixing or injection (one temp). I have a Honeywell strap on aquastat wired to a burner cut off contact to protect the floors from a control malfunction.

    The problem with 194 degree dhw hx supply temp is that when I switch from dhw back to heating there is a very hot slug of water that has the potential to trip my 130 high limit. fortunately the low mass of the boiler and slow response of the strap on make this not that much of an issue.

    Still I'm more comfortable operating at a temperature that is a bit lower, the Tekmar control allows adjustment of this. I'm not having a problem with 165 in this particular situation. I'm also comforted that I'm staying within the condensing threshold and perhaps working the boiler a bit less hard as well as limiting the potential for accelerated thermal breakdown of the glycol.

    All glycol is not created equal, and even a very stable high quality glycol can be effected by bad water chemistry. My understanding is that aluminum does not handle acid conditions well which I must admit concerns me a bit since the combustion side of the hx is exposed to acidic condensate.Some speculate that the usefull life of these exchangers may not be much longer that their 10 year warranty. Even if this is true the price difference between this boiler and it's German competitor make the prospect of a hx replacement at 10-12 years almost acceptable to me.

    Standard glycols have the potential to hydrolyze and become acidic,this is accelerated by high operating temps. A real issue in solar systems that can periodicaly reach very high temps.
  • Karl_4
    Karl_4 Member Posts: 11
    GB boiler heat exchangers

    The problem I've seen is the aluminum heat exchangers being totally eaten away. When contractors have gone to check they've found the condensate trap full of aluminum. I know a couple instances where guys didn't use aluminum safe antifreeze but there are numerous ones that did use the right antifreeze. Buderus wasn't always specifying which type of aluminum safe antifreeze to use but now they are. What is the difference in the brands and why is this happening? Is it the fill water, ph or something? Should we be using distilled water instead? I know in my area guys are switching to stainless steel boilers to get away from this problem.
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