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Radiant Floor Heating/Buderus- Onyx compatibility


First installed in 2007 I have a high efficiency wall mounted Buderus for my radiant system using 2 loops of Onyx tubing.
Since then I have had to replace the furnace twice because of corrosion. The last time the rep told me that the problem was that the supply water was softened. We added a direct line to the city water.
That furnace now is clogged again and I'm afraid it is going to fail.
Any thoughts would be appreciated

Badger Boiler Buderus corrosion
Badger Boiler Buderus  
Hello Ross,

Sorry to here of your Buderus boiler problem. You may certainly be suffering from bad chemistry, which has caused many a heat exchanger (HX), both aluminum and various stainless steel HXs used to build high efficiency condensing boilers.

The Buderus GB142 series has aluminum HX, this is not necessarily a bad thing, but aluminum will not suffer high alkalinity without serious corrosion, which will eat the HX from the outside in. Clogging delicate control mechanisms and in the worse cases clog near-piping and radiant manifolds completely.

We have serviced troubled Weil McLain Ultra condensing boilers (also aluminum HX, but entirely different supplier) and found water treatment to be just as critical.

Here in Minneapolis we test the chemistry of every boiler we perform annual service on and flush, clean, flush again, and fill with hard or naturally soft water and then treat the water, a.k.a. heat transfer fluid with non-toxic inhibitors. This treatment will raise the pH to a slightly positive level to accommodate condensing and non-condensing boilers sporting stainless steel or cast iron HXs that do not like low pH AND condensing or non-condensing copper and aluminum boilers that will not tolerate high pH.

In all cases you must follow the manufactures' specification for approved additives and test annually to make sure they are maintained.

We have had particular trouble with aluminum HX from 3-7 years back charged with the wrong anti-freeze causing them to fail prematurely. Once corrected or never exposed to aggressive water, we find the they hold up well and transfer heat quite efficiently if maintained regularly and properly.

If you use any kind of radiant floor tubing other than those meeting the DIN standard for PEX including an effective oxygen barrier, you must check the pH and general water quality more often since oxygen is not good for any hydronic system and fresh water is full of oxygen so fix the leaks and fill only when you must.

We use a power-flushing machine to clean every system we find compromised by heavy corrosion.  

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Morgan M. Audetat


Radiant panel heating design, including floors and ceilings, European wall panels and snow melting for residential and light commercial buildings..............................................................-Master of Steam and Hot Water,City of Minneapolis....................................................--- Master Plumber, State of Minnesota...........


30 years..... Charter Board Member - Radiant Panel Association, former manufacturer of condensing boilers, former national distributor of radiant floor products, son and apprentice of mechanical & plumbing contractor. Current mechanical/plumbing contractor specializing in hydronic based, integrated HVAC systems. Radiant floor heating/cooling. Snow Melting. Condensing Boilers. Indirect water heaters. System design, consulting and technical training world-wide. Licensed contractor, designer, installer and consultant.

B.S. University WI 1981 CONTINUING EDUCATION: Viessmann Condensing boiler and Solar water heating certification 2010, N.D.S.U. Lead Worker RRP certification 2010, Knight condensing boiler certification 2009, Wrightsoft Manual J CAD certification 2009, RPA Designer & Installer Certification 2008, Nate Hydronic/Forced Air Certification 2008, Uponor/Wirsbo advanced design school certification 2007, Buderus Wall-hung certification 2007, Power Limited License (low voltage controls) 40 CE credits 2005, Basic Hydronic Certification IPEX & Northern Alberta Institute of Technology 1998, Charter Board Member - Radiant Panel Association 1994, Residential Off-Electric to Hydronic Conversion Heating School Canadian Hydronics Council 1994, B&G Little Red School House 1993, Rood Utilities (now Auburn Technical Institute) Oil Burner School 1993 ,Tekmar Controls residential and commercial 1993, Division Manager and Advanced Hydronic Seminar Instructor for the first Exclusively Hydronic Radiant Floor Distributor in the USA 1990, Hydronic Radiant Heating Association Workshop participant with Richard c. Bourne, PE spring 1988, Master Plumbing, Hydronic, Solar Course Red Rocks Community College 1987.

Awards and Honors
2009 System Showcase Award - Radiant Panel Association

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