barnabas1969

I am currently seeing exactly the same problem on my house in Florida. Code requires a new water heater to be installed with an expansion tank. My house was built in 1961, before code required back-flow preventers. I installed a new water heater not too long ago and because I'm a good guy, I did it per code. I even adjusted the air pressure in the expansion tank to match the water pressure per the instructions included with the expansion tank. My water meter has a small wheel with a red triangle on it. With everything turned off in the house (including the valve to the RO system), I can see the red triangle turn forward a little bit, and then backward a little bit. However, it doesn't turn as far backward as it does forward. My meter slowly moves forward. I've read that some meters will read reverse flow while others will now. However, NONE of them will ACCURATELY measure reverse flow. So what is happening is that the water main pressure is fluctuating causing the expansion tank to expand and contract. The water flows in and gets measured correctly by the water meter. Then, it flows back out and gets incorrectly measured. The net result is that I am paying for water that I am not actually using. I have verified this using the same method that the original poster did... remove the expansion tank. So... this weekend I will be installing a dual check valve at the meter... which I purchased for a whopping $22.00 at Home Depot. It should pay for itself in just a few months.