This site is great help.

I have problem with hot water pipes so I had to shut off the main water from outside. My question is,do I have to shut off my electric boiler from the cercuit braker?

Thank for any advice.

You may not have to, but depending what all goes wrong, it might be a good idea. You can have problems if the heat comes on when the boiler is low on water. Likely it would hold its level without make up water, and even if it didn't, it would have a low water cut off.

Thank you for the reply.