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Backflow Preventer vent drip (hot water heating system)

hello all

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?


Re: Backflow Preventer vent drip (hot water heating system)

Sounds like your backflow preventer is going. Repair or replace.

Re: Backflow Preventer vent drip (hot water heating system)

I would definitely call in a pro to look at this (your boiler service person), rather than speculate what is now causing the constant leak thru the drain tube.

The Watts 9d-m3 backflow preventer valve is widely used in residential applications, but there has been loads of problems over the years with their operation because they have an atmospheric vent tube that can start dripping water for a number of minor reasons, such as a small piece of accumulated crud stuck in the valve seats, or a minor clog in the upstream inlet screen.

If you attempt a diy job to disassemble to clean or replace the valve you may have to go thru a boiler shutoff/draining procedure, and depending on the piping arrangement in place, you could easily end up with boiler water all over the boiler room floor.

For someone in your situation where the house is used as a vacation home and it is advisable to turn the supply water off when vacant, there are non-venting backflow preventer valves that are more widely used these days, providing the local code allows their use in your area; more & more local jurisdictions are now allowing the non-venting bfpv, especially in residential applications in view of the headaches the venting versions are causing; talk to your boiler service person about this option before the present unit is replaced with one that can easily start leaking down the road again.

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