Grant Erwin wrote:
I have a 10 year old hydronic heating system in my home. There is a
boiler and it leads to a special tank which holds the heated water,
which is circulated on demand through wall registers. The thing that
makes this tank special is that it also holds potable water, i.e. a hot
water tank. The heating and potable water never mix, ever.

My tank has developed a pinhole leak right up on the domed top. I cannot
imagine that there wasn't a manufacturing defect, but the warranty says
that if the house is sold the warranty ends at 5 years. Before I buy a
new tank at a whopping $1200, I want to at least try to fix the pinhole.
My heating system guy shook his head and said "it would never hold" but
I don't see how I have much to lose. There is almost certainly some kind
of liner which I'd have to worry about, so I'd want to use minimum heat.

Anyone have any idea how something like this might be patched? I was
thinking of trying a soft solder perhaps.

GWE
Depending on how hot this gets, you might be able to epoxy it.
What is the tank made of? Galvanized steel? You have to get the
area near the repair dry on the inside to get it hot enough to
solder. It may be very difficult to get the 10-year old surface
clean enough to solder well. Make sure there is no trapped water
in the tank, or you could have a deadly steam explosion.

Jon