Steve wrote:

Hi, I live in Long Island, NY. My current heating system is a 50+ year
old American Standard boiler with a Beckett oil-fired burner. Attached
to it is an uninsulated indirect water heater of unknown brand (which
is probably as old as the boiler). Most of the system is as old as the
house, which was built in the early 50s (the burner and a couple of the
circulators are fairly new).

For some reason, the previous homeowner (who was also the homebuilder)
connected the indirect water heater to the hot water coil of the
boiler, rather than using the recirculated boiler water. The system had
been working fairly well, although I suspect not at top efficiency (we
had insulated the water heater using a fiberglass water heater blanket,
but there was still some heat leakage out the top).

Anyway, recently, we've been having problems with the boiler pressure
triggering the pressure relief valve. After I empty the expansion tank,
the pressure gauge goes down to a more reasonable level; a couple of
weeks later and the pressure is high again. Our serviceman came out and
told us that there is a crack in the hot water coil (I'm not sure how
he concluded this, as I wasn't home at the time, and I didn't think to
ask).

SNIP

The other possibility is that the boiler feedwater valve is leaking
(i.e., not closing tightly) allowing a trickle of water into the
boiler day and night. Look for a shutoff valve so you can isolate
that as a cause.

former LI'er