PARTICULARS - boiler works to heat the house and supply hot water, system is about 15 years old with no significant problems to date.
the cold water supply line feeds into a WATTS 1/2" 9d-m3 backflow preventer with intermediate atmos vent, that then feeds into a WATTS #S1156F pressure regulator.
PROBLEM - i noticed that when i turn the house water supply off a small amount of water drips from the vent on the backflow preventer, this usually stops within a few minutes. last night i turned the water on without incident but now the backflow preventer keeps dripping water and will not stop.
this is a vacation home so lately we have adopted the practice of shutting the water supply off when the house is vacant. any ideas on what suddenly caused the backflow preventer vent to drip non stop?