You can try this too. alot cheaper if it works. Try it on one, just don't break off the set screw and you can return it. Could be a # of things but this is where I'd start before getting too involved in a costly repipe if it's not the problem.
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8
Hose Connection Vacuum Breakers, Brass
Size(s):
3/4 in. (20mm)
Description:
Series 8 Hose Connection Vacuum Breakers permit the attachment of portable hoses to hose thread faucets and prevent the reverse flow of polluted water into the potable water supply due to backsiphonage. It consists of a brass body construction, stainless steel working parts, and a rubber diaphragm and disc. Series 8 is ideal for inside and outside, health hazard installations requiring non-continuous pressure such as service sinks, swimming pools, photo developing tanks, laundry tubs, wash racks, dairy barns, marinas, and general outside gardening uses. Check with local inspection authorities for installation requirements. Maximum Pressure:125psi (8.6 bar).