After the electric water heater was unplugged, the water inlet valve was forgotten to close, and the weather was too freezing. What happened?

It is normal for the cold water pipes to freeze because of the weather, which has nothing to do with whether the inlet valve is closed or not. It is unnecessary to close the water inlet valve. It is only necessary to close the water inlet valve during maintenance, and it is more difficult to freeze without closing the water inlet valve.

The solution is only if you know it's frozen there and thaw it with warm water, otherwise you can only wait for the weather to get warmer.