Pressure drop when water shut off

[Pushc5]

So I recently installed a flo sensor by moen. It has a feature to detect leaks. When I turn it on it says water was being used or there was an error due to thermal expansion. I’ve tried several times always the same result.

I manually shut off the valve and it started at 53.3 psi and 12 minutes later it was at 47.6. When I turned it back on it was reading ~.3 gpm for a couple seconds but I couldn’t tell where it was going.

I checked my hot water expansion tank and it has 53.5 psi in it currently and sounds hollow at the top.

I checked all the faucets I don’t see any leaks. Nor have I heard any toilets running. Anyone have any ideas?

I did get one passed test after I showered, but tried to reproduce by running hot water for a while, letting the hot water tank fill up and then shut the valve but it still showed dropping pressure. I know a faulty expansion tank can cause pressure increase but what about about decrease? I already tested to see if the pressure drop was across my softener and filter by closing the valve after those tanks and the test passed with those closed.

 

[Ryan Symons]

Toilet fill valve. You won't hear it when they don't completely shut off. It just slowly fills the tank and then down the overflow.

 

[Sponsor]

 

[Pushc5]

Toilet fill valve. You won't hear it when they don't completely shut off. It just slowly fills the tank and then down the overflow.

Oooh I’ll give this a look tomorrow! I’ll go toilet to toilet and shut off the water and see if that stops the pressure drop. Thanks!

 

[Jadnashua]

are you on a well system? The check valve in the well could be leaking.

 

[Ryan Symons]

are you on a well system? The check valve in the well could be leaking.

He said it held pressure when a valve after the softener was shut off. This eliminates that as a possibility.

 

[LLigetfa]

I know a faulty expansion tank can cause pressure increase but what about about decrease?

The opposite of expansion is contraction so the hot water it the lines cooling off might cause a slight decrease in pressure.

I already tested to see if the pressure drop was across my softener and filter by closing the valve after those tanks and the test passed with those closed.

Where is the pressure read in relation to the aforementioned valve, before or after? If after, then the softener could be leaking to the drain or leaking back to the source. Is the source a well or municipal?

 

[Pushc5]

Thanks Ryan Symons, ended up being a fill valve on one of my toilets. It's crazy I couldn't see or hear it when I was staring right at it. Shut off the valve at that toilet and everything pressure tests fine. Ordered a replacement!