View Full Version : leaking backflow preventer

05-24-2007, 06:09 PM
Have 4-zone h.w. baseboard system. Hydro-Therm furnace piped according instructions has worked fine for 15 years. Recently, the backflow prev. atmospheric vent began to discharge a small but significant amount of water. City w.p. is 60psi (regulated). Supply goes to backflow preventer > auto fill/regulator > furnace. There is also an exp. tank in the loop (new). All the parts listed are new, Watts brand. After new backflow prev. installed, water flow from vent has been reduced but not stopped; dripping steadily. Furnace pressure when firing is high, 16-18 lbs. Hydro-Therm support agrees operating pressure is high but had no real solution to offer.

05-24-2007, 06:21 PM
The expansion tanks usually come precharged reasonably close to where they should be, but you might want to check. To do that, you have to drain enough water out to relieve the pressure, then you can check the air pressure. It should be around 15 pounds. If it isn't, add some. Is the pressure-relief valve new, too? They can wear out or get sticky when they get old.

05-24-2007, 11:59 PM
Tank was installed new after the leak started but I had checked the pressure anyway just to be sure. It was at 24 lbs. Thanks - will change relief valve just in case.

05-25-2007, 04:54 AM
AIUI, the expansion tank pressure should be approximately equal to the system operating pressure. Also, typically gauges might not be (probably aren't?) calibrated so some error (difference or variation) might be expected.

On the vent discharge: There is water coming out of the vent and you've changed everyting but the vent. Water continues to come out of the vent. When is the vent going to be tested/changed?

05-25-2007, 12:31 PM
Thanks, CHH. I should have been more clear. The leak is from the atmospheric vent on the b.f. preventer, not the pressure relief valve on the boiler. Today the leak seems to have stopped on its own, no thanks to me.

05-25-2007, 12:48 PM
When I reread your initial post, its clearly stated that the vent was on the backflow preventer. I just read "vent" and assumed it was the system vent. My mistake.

Glad to hear the drip cleared up.