copper pipes-in-ceiling system clogging-up

Luke_7

Have a radiant hot water system consisting of 3/8th inch copper piping in ceiling over metal lath/plaster in companion with 1" steel piping in basement slab installed 1954. Steel floor system failed in 2007 and was valved-off (really miss that!). Only maintenance to wet side of system is periodic, usually annual, bleeding-off of trapped air and on again-off-again phosphate feeder in main domestic water supply. No "special' or exotic chemicals ever added. Suspect one circulator may be losing some lube oil to the wet side.  The hot water is slightly rust colored and pH is 6.7 ( 6.0-7.0 pH annual readings unchanged for 30+ years).

This year, for first time, annual air bleed revealed 2 or 3 zones that would not bleed. Applied mild vacuum and got them draining/flowing  and collected about a  pint sample of rusty water which eventually sorta cleared up when left undisturbed for 2 + days. The sample yielded about 1/4th teaspoon of iron to a quarter-sized samarium magnet attached to outside of glass sample jar—a presumed legacy of now-dead iron-side floor heat. Also a thin layer of brown gunk/sludge settled out on bottom of sample. In the meantime, touching all return lines at the 2 intake manifolds showed the lines from the zones that initially did not bleed  were lukewarm or cold--indicating blockage.

 I plan to drain the entire system come warm weather-- hopefully purging the rogue iron particles along with any sludge. Obvious question--is there anything that can be done now or later to unclog the blocked lines and restore flow--and prevent this problem from recurring? Thanks for your input.

SWEI

I'd start with

A pressure integrity test.  Check the expansion tank, possibly replace.  Is there an auto water feeder on this system?  If so, turn it off and see how long the system holds pressure.  If you're losing pressure, you need to find and fix that first.



Next, a good power purge -- run city water pressure through the zone until the water comes out clean.  I'd pull the circulator and examine other components to see if they suffered any damage.  Repair/replace if necessary, then fill with water and some Rhomar 9100 and run it for a week or two.  Drain, possibly repeat, depending on what comes out afterwards.  Refill with 922 (should bring your pH up a bit) and run for a season.  See what the water looks like at the end of that season.  It should be squeaky clean.