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Thread: Boiler System Cleaning Agents - Which One?

  1. #1
    DIY Junior Member robinasu's Avatar
    Join Date
    Nov 2011

    Default Boiler System Cleaning Agents - Which One?

    Background: Our condo building hydronic heating system was essentially neglected for 10 years before I came around. About a year ago our Ergomax reverse indirect and cast iron boiler were replaced as they were in pretty bad shape.

    Our 5 wall radiators never worked well and the contractors essentially gave up. I started poking around and did some head loss math: the tubes to the radiators (which are on the bottom floor of 3) had to be clogged. Three quarters of a bucket full of iron oxide later I was getting good flow. I flushed the system. That was about 6 months ago.

    Last weekend I checked the wye strainer and hydro seperator. There was a bit of flakes and sand (mainly iron oxide, I believe). Our 12 radiant floors (about 10k BTU/h each) are flowing. It's unknown if any iron oxide are in the floors. I scanned 4 of the floors (2 on level 2 and 2 on level 3) with an IR camera and there did not appear to be any blockages. The hydronic piping is copper and pex, brass fittings and valves, stainless boiler HX, iron pumps, and no iron pipe.

    Based on calculated pressure drops, I believe there is significant scale in the radiator distribution piping, and there is probably iron oxide pooled in spots.

    TSP seems like a decent option, as well as chelating agents. I've seem the Rhomar products. Can you please give me your thoughts on the best treatment strategy and products?

    If I could safely dissolve the iron oxide and scale, then flush, that would be awesome. I'm done with the air compressor and water hose method!

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sep 2004
    New England


    WHen there's a leak in a hydronic system, the frequent addition of fresh water is a likely reason for excessive rust. WHen there aren't any leaks, whatever free oxygen that there may be in the fresh water used to fill it, quickly causes rust, then, there's none left to continue that, so it will remain stable for a VERY long time, unless the exterior of the pipe gets wet and it rusts from the outside in.

    Can't help with trying to clean it out other than flushing. I'm interested in what the pros have to say, but it sounds like you need to get your leaks in check.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3
    DIY Junior Member robinasu's Avatar
    Join Date
    Nov 2011


    Agreed. I've scoured the system and I can't find any. They may have been fixed when the boiler and near boiler piping was completely replaced. When I checked the water last weekend, it was still clear, although there was some what I believe is iron oxide sand and old boiler heat exchanger flakes. System pressure is also constant when I turn off the makeup water. I believe the main source of oxygen has been sealed. I also believe there may be a decent amount of scale that could be removed. I still need to check the pH.

  4. #4
    Master Hot Water Mpls,MN BadgerBoilerMN's Avatar
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    Mar 2011


    We have been seeing many more residential hydronic component failures in recent years, as the pieces and parts of modern boiler systems are increasing European in nature i.e. smaller and more precisely machined. Add to this, the system flow switch, low water cutout and capillary pressure switch found on most high efficiency condensing boilers and you have the makings of a nuisance lock-out, just about every season if the water/heat transfer fluid is not carefully selected, injected and maintained.

    What you describe is an extreme case and as suggested may be due to habitual filling of the system with fresh water.

    To wit, we finally decided, last year, that flushing our new, and old, hydronic systems, many of which include radiant floor manifolds, thermostatic radiator valves and sophisticated mixing devices, was just not adequate. Now we find many older systems must be power-flushed, filled with the appropriate water and treated for corrosion. We found the people at Fernox have the best system for this and use their products on every hydronic heating system we install and nearly everyone we service, be it residential or commercial. The results are impressive. No rust, corrosion, air or noise with increased water-side efficiency.

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