when water heater should have expansion tank

[Amir Faghih]

I need clarification as to when there must be expansion tank near water heater.
I understand, that if there is pressure regulator in front of main water meter, then there must be an expansion tank for water heater. BUT, new generation of pressure regulator eliminates the need for expansion tank. Is that correct?
Thanks for your help.

[Bob Elliott]

Anytime there is a booster pump or check valve for instance unless you like the tpr valve tripping

[James E. Braun, CMI]

It is mainly a code requirement. Usually in my area you can install expansion tees instead of tanks.