I am grateful Rick took the time to document and post his corrosion issue and how he corrected it.
When I first saw Rick's photos he was well into the process of cleaning under Mike's (Precision Chem) guidance. I was upset at learning that Mike had concluded that boiling the unit had been a contributing factor to the above water line corrosion. A year earlier I had told Rick that a boil resulting from an overfire was mostly a nuisance to be avoided... that if it happened once he was unlikely to do it again as he would learn the characteristics of his system. I think I suggested not reloading at over 180 as a starting guideline.
I was particularly discouraged when Rick told me that he had a bio test done just before discovering the bacterial corrosion and that it had come back clean! We recommend twice a year visual inspection and water testing and we send reminders out with the belief that that schedule will head off any serious corrosion issue. I spent quite a bit of time on the phone with both Rick and Mike trying to understand what had gone wrong here. Like Rick I couldn't get my head around the negative bio test. I now believe I understand it, but I'll get back to that.
Corrosion is about the only way a GARN can be damaged. The owner's manual talks at length about different types of corrosion issues and the need for water testing and visual examination of the tank. The type of bacterial corrosion above the water line that Rick experienced after boiling is not common. Dectra is very forthright in the manual about the potential for and causes of corrosion issues. If over-firing and boiling had been understood to be a common cause of the type and degree of corrosion Rick experienced, the manuals would have addressed it. Common or not, the newest manuals now do address it.
The new digital GARN controls have been shipping for about month or so now. The new control has the following language on the front cover:
Notice: DO NOT OVERFIRE! If the tank temperature exceeds 200 degrees F or steam is visibly discharging from the overflow pipe or the manhole cover – you are OVERFIRING. There is no danger of explosion. However, higher temperatures significantly increase water loss from the unit and may initiate moisture damage within your building or shed. Steam as a result of over-firing may significantly increase corrosion.
Every new GARN is now shipped without water treatment chemicals, but with a water test kit. The owner is instructed to submit a water sample before filling their tank. Chemicals will not be shipped until that sample has been received and processed. This allows Precision Chem to make individual adjustments for unusual water issues, to get the owner into the testing routine and into Precision Chem's data base.
Additionally, in our territory emails or postcards are sent twice a year reminding GARN owners of the need to maintain testing. The GARN owner's manual devotes several pages to the potential for corrosion and the critical need to maintain testing and good water chemistry. However, for some reason only about 1/3 of GARN owners avail themselves of the testing program, 2/3 do not! I'd guess that compliance among Hearth readers is much higher
I had a phone call the other night from a GARN owner in New Brunswick who suggested that if a GARN is not going to be fired for several months fill the GARN unit to the manway ring thus fully wetting the top surface inside the tank. Heaterman then made the same suggestion. The information that Heaterman posted in #89 clarifying the over-firing issues was really good and I'd suggest that every GARN owner print it as a reminder.
As to that reference in the manual relating that 9% of GARNS have experienced a corrosion issue, I'm told that that number is high and out of date. Apparently in the 80's environmental concerns eliminated many earlier water treatment options and until safer treatment methods were developed there were industry wide boiler corrosion issues. That 9% reflects those years. As bpirger pointed out that statement also does not mean that those 9 out of 100 GARN units were destroyed.......it means they experienced a correctable corrosion issue.
I mentioned earlier that I was really troubled that Rick's bio test, done just before his visual assessment, had failed to detect contamination. After re-reading Rick's post I realized that he had drawn the water sample from a point in his basement 170 feet from his GARN and that the circulator had not been run since the previous heating season. The water that Rick drew was pretty much isolated from the soup that was brewing in his GARN so now the clean test doesn't surprise me. It also reinforces the need to collect the sample through the manway and do a visual check at the same time.
Finally, I never cease to be amazed at the volume of collective and supportive knowledge that exists in this forum. Hopefully, we have all learned much more about water chemistry, biological contamination and corrosion as a result of Ricks experience and this discussion. Thanks to all of you.
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