One for the professionals

Yesterday my neighbor approached me with a plumbing problem (I am a licensed plumber). They told me that their water bill has almost doubled and their electric bill went up. At first I thoughjt this was a no brainer, an under slab hot water leak. However when I began checking it out I noticed that the hot water has already been rerouted overhead. The water heater had a tapping sound originating in it and the cold water pressure was fluctuating at the kitchen sink. Turned off the valve above the heater and the tapping stopped and the water pressure at the kitchen sink equalized. Turned the valve at the water heater on the tapping, fluctuating resumed and the water meter ran at about 1 gallon/min. Turned the valve off and the meter stopped.
I put a pressure gauge on the hot water at the laundry tray and turned off the valve at the heater, the pressure did not drop as expected. However I did notice low water pressure (25 psi). I then put the gauge on the hose bibb where the water enters the house, the incoming water pressure was 25 psi. I adjusted the PRV to 50 lbs. Now all the symptoms have stopped. The pressure no longer fluctuates at the kitchen (it was actually fluctuating throughout the cold water side), the tapping at the heater has ceased, and the meter no longer runs.

Has anyone run into a similar situation? Can a faulty/low setting on the PRV cause such problems? Been plumbing for 16 years and this is a new one on me. That's what I like about plumbing, no matter what you have run into, you havn't seen it all yet.b

??

None of that would explain an increased water and electric bill.

Dumb question from a non-plumber

How does a PRV work? When it relieves pressure, where does the water go?

A PRV doesn't relieve pressure, it reduces it Pressure Reducing Valve PRV.

The fluctuating water pressure seems to have been caused by a worn ballcock. The toilet had a leak through the flapper, but doubt it was enough to double the water bill but who knows. Anyway after repairing the toilet and adjusting the pressure everything appears fine. The water meter didn't move for 30 min so everything is fine now. Don't have a clue why the electric bill went up so much. It's funny how the meter originally ran and stopped as I turned the valve on the heater on and off.

This might be stupid, but could it be that if you had a single lever shower valve, and it had really low pressure at first and the heater jacked up the pressure (from some kind of thermal expansion maybe? ) on the hot side when the water heater was on, and it bled through the single lever shower valve to the cold supply on the shower, and to the toilet? Cause you know how sometimes you'll be working on a hot pipe and the lady of the house runs some water on a single lever faucet and you cuss like crazy because now you have a half soldered pipe full of water.
Perrycat
PS....to take that one further, why do you sometimes put in a water heater and you go to fill it up, you've put on a new shut off valve, and turn the water to the house back on, and the heater starts filling up even with the heater valve turned off.....single lever faucets? or did somebody cross somethng when they piped the house?
perrycat

Let me rephrase the question...

How does a PRV work? When it reduces pressure, where does the water on the low-pressure side go? Or does it only work when there's a flow?

Mikey,
Check this out http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learnabout_wprv.htm

also, this one was not there but if you ever need to look common household things up check out the www.howstuffworks.com site. it has some pretty cool stuff on there explained in words normal folks can understand.

Prv

It works all the time unless it is broken. When water is flowing, it only lets enough water through to maintain the set pressure. When there is no flow, it shuts off and just maintains the pressure in the downstream side.

Thanks, Gouranga, for the link; this all makes sense now.

-mike