We have an old ( circa 1972 ) Crown Boiler for hot water and heating.
About three weeks ago, we started hearing running/rushing water sounds in the baseboard heating pipes when any of the zones turned on. It last about a minute or two, then we hear the regular moans and groans of the baseboards. The rushing water sound is new. This only happens with the heating zones, not the household hot water supply.
Any ideas would be appreciated.