3/4" copper pipeing through out house.

The city water co. installed a water meter in the house ,I now have air in the pipes and the electric hot water heater blow off valve keeps blowing off. Had no problem before meter was installed.

Water heater is only 2 months old.

Was told by the meter people that this sometimes happens and I need to install a expansion tank.

Is this correct or is there another,simpler,

solution?

Would a Air water separator placed in the line between the meter and hot water heater work?