Today when I cut out a bunch of old hot water baseboard units I noticed that the water, when it would drain from the heating element, was disgustingly BLACK, that is coal black. If I smeared my pinky inside the pipe to feel the interior my finger would come out black as tar and it would stain my finger that only a good Lava scrubbing would get out. Sorta like the black stain you get when you touch a deteriorating rubber toilet tank seal. This black water was only present in the horizontal runs of the elements, that is I’d cut off the elbows from the elements, pick up the element and dump it into a bucket.
Later, when I went into the crawlspace to make the new joints down below, when I drained water from the horizontal line the water was quite clear.
The HO I replaced these hot water BBs for had complained that they were no longer getting heat into the rooms for the units I replaced today. They said they’d feel heat on the pipe, but very little radiation of the heat from the old units. Also, when we removed the old units, we noticed that the pipe on which the fins were was a dark black with the occasional green oxidized “fuzzy” along the length of the fin pipe. A few places we saw green oxidized stains on the carpet underneat the fin pipe as if the pipe were leaking somehow causing some of the oxidized coppper to leak with it staining the carpet. Yet there was no signs of any leaks in the pipe.
I was wondering, what is the black water (since when does copper blacken water), and can it have something to do with somehow preventing the pipe from transferring heat to the fins thus being the cause of the HO that the rooms wouldn’t heat anymore?
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From my experience, black is the normal color of water in a closed hydronic heating system. Smelly too. This is the 'equilibrium' state. Initially, the water is 'hungry' for minerals and loaded with oxygen. It sucks some minerals out of the plumbing until the oxygen is removed by the air scoop. Then the corrosion process stops.
Black water does not point towards a problem by itself.
The external corrosion could be from condensation in the summer, some point in the past whe the sytem was run over pressure, or an actual slow leak.
Edited 10/15/2005 11:59 am ET by csnow