No need to replace parts that are working. Symptoms of an electric WH not working would be quickly running out of hot water or really long time to recover.
You might want to check and replace the anode rod (assuming this has a metal tank...if it's not, then there won't be an anode rod to replace). Those are more correctly called sacrificial anodes, and they literally get eaten up in preference to the steel in the tank, but when they're gone, the tank starts to rust. Most people don't change them, and then the tank starts to degrade. They're used in numerous situations including boats to keep the hull from disintegrating.