Sosh

Hi, I believe I'm seeing exactly the same problem as Lasswell and Barnabas1969. Background - we recently moved to a new house, and soon realised that our water bills were astronomical. We assumed a leak but have not been able to find anything. We switched off taps to all toilets and fittings that we could, but could not identify the problem, and no sign of leaks anywhere. However according to the meter, we were using about 6 Litres of water an hour even though nothing was on. I noticed while watching the water meter that when there was nothing running the it would slowly drift backwards and forwards. My theory was that perhaps the mains pressure is fluctuating slightly, and the expansion tank is pushing water back through the meter during the pressure drops. That combined with the possibility the meter does not measure backwards accurately. Reading this post has made me think this is the most likely explanation. However, there is a check valve and PRV in line before the water heating system with the expansion tank - so this has me stumped. @Barnabas1969 - did the installation of the double-check valve at the meter solve your problem? Thanks, S