It can certainly flow backwards against the mains if the pressure is higher but whether it would turn the meter in reverse or not, don't know.
Have you got a pressure gauge mounted anywhere after the NRV?, say on the cylinder itself?, if you have, then as the cylinder is cooling down and with no usage the pressure should start falling, if it doesn't then it points to the PRV increasing its downstream pressure.
Wthe temperature falls from 60C to 50C then the pressure would have to rise by ~ 0.4bar to increase the water volume by 1.85 litres (per meter reading).
Have you got a pressure gauge mounted anywhere after the NRV?, say on the cylinder itself?, if you have, then as the cylinder is cooling down and with no usage the pressure should start falling, if it doesn't then it points to the PRV increasing its downstream pressure.
Wthe temperature falls from 60C to 50C then the pressure would have to rise by ~ 0.4bar to increase the water volume by 1.85 litres (per meter reading).