1.It sounds like an indirect water heater, and doesn't heat your radiators.

2. They are usually coated steel, (porcelain), any welding will further
damage the coating. What brand is this unit? How old is it?

3. As others have mentioned, fix one spot and you'll play little Dutch boy
with more leaks.

4. If the whole thing goes while your away you'll flood your basement.
Consider this a free warning

5. Next time replace the zinc anode inside the tank every 10 years or so, if
it is accessible.

Tony



"Grant Erwin" wrote in message
...
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