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Baxi Return Line corrosion

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Mark_Russell
Mark_Russell Member Posts: 5
in Gas Heating
Grateful for any thoughts on possible causes of the corrosion on this 3 year old Baxi boiler. This is the return line just before it enters into the fired part of the boiler. It’s an open system; the pump is just upstream and the F/E tank line is just downstream (of the boiler) We installed to replace the original gas boiler that was 15-20 years old and had no signs of corrosion (at least externally). The heating system was zoned at the same time we had the boiler replaced and we have a serious high point in the downstairs loop. Any thoughts are appreciated 

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  • mattmia2
    mattmia2 Member Posts: 9,639
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    Open systems and ferrous components don't play well together.
    Derheatmeisterkcopp
  • Mark_Russell
    Mark_Russell Member Posts: 5
    edited May 2021
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    Ok. But 3 years for stainless steel to corrode to that degree seems fairly aggressive? Are there non-ferrous alternatives on the market? My main fear is that when we replace the boiler we’ll get the same result.... which could turn into a rather expensive boiler replacement routine
  • mattmia2
    mattmia2 Member Posts: 9,639
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    That tube doesn't look like stainless. Is it supposed to be? It is so crusty I can't tell if the tube is leaking or its connection is leaking.
  • mattmia2
    mattmia2 Member Posts: 9,639
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    Not knowing specifically which model that is, the first baxi boiler I picked is clearly designed for use in a closed system only. If you need to heat an open system, your best bet is to do that through a heat exchanger with components rated for an open system (bronze/stainless pump, open system expansion tank, nonferrous piping, etc.) on the open side of the system.
  • Mark_Russell
    Mark_Russell Member Posts: 5
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    Pretty sure that’s the stainless return line (it’s inside the boiler - picked up during the annual service). There’s no fitting.... i think it’s weeping right on the bend - I assume it’s pitted on the bend from the inside out. 
  • Mark_Russell
    Mark_Russell Member Posts: 5
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    Handy drawing in the Baxi manual. Highlighted yellow shows the return line in question. Badly drawn red arrow indicates the bend where the corrosion was found 

  • mattmia2
    mattmia2 Member Posts: 9,639
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    I don't see any reason for that to be stainless. It is on the water side of a heating boiler, it isn't exposed to the corrosive products of combustion and would be much more difficult to fabricate in stainless.
  • Mark_Russell
    Mark_Russell Member Posts: 5
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    The boiler is an ‘ecoblue advance hear’ and the manual states suitable for use in an open system. Can’t find anything to confirm materials of construction 
  • mattmia2
    mattmia2 Member Posts: 9,639
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    It looks like it requires an inhibitor in the system. If that is the case and that wasn't being maintained properly, that could be the source of your corrosion.

    I didn't know what type of system this was and I think this is a european system. Open expansion tanks are very uncommon on modern systems here.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,520
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    @Mark_Russell

    Does it have to be an open system? You have better results if it was closed
    mattmia2
  • kcopp
    kcopp Member Posts: 4,432
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    Can we get a picture further back?
    You may be able to replace that part.... If it comes out ok.

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