Backflow valve installed, water pressure build up


Last week the county replaced my water meter and installed a backflow valve. In preparation for this six months ago I had an old pressure reducing valve replaced and a thermal expansion tank installed on my water heater by a master plumber.
Since the backflow valve has been installed I am seeing my water pressure steadily increase after I stop using water. For example, I will run the water and I see about 48 psi water pressure. After 20 minutes the pressure will increase to around 60 psi. Two hours later it can be up to 80 psi. After a night's sleep the first flush of the day is very high powered but I have not stumbled outside to test but it has to be at least 80 psi if not more.
Does this sound normal or is either my pressure reducing valve or expansion tank not working properly?
Thanks - Frank
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On Jul 2, 5:35am, snipped-for-privacy@gmail.com wrote:

Normal for pressure to increase in a closed system due to thermal expansion from the water heater. This is only short lived until the system is relieved of the excess pressure then it starts again.
kenny b
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