replying to J.Albert, Iggy wrote:
I'm not an HVAC tech, but no, the system is closed so it should still be
pretty much new inside of everything...so I wouldn't suspect and haven't ever
run into a build-up issue. What I suspect the problem to be, is with your
Expansion Tank. Either the tank's failed or it lost pressure and is no longer
functioning.

Put a manual tire pump on the Expansion Tank's Schrader Valve and pump it up
to just 7psi. It'll either hold and you fixed the problem or the air will
bleed back out through the Hy-Vent and the problem will persist until the
Expansion Tank's replaced. And yes, 30-years is a boiler's "average" lifespan,
some last less and others go a whole lot longer.

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