Bosch Tronic 3000T ES2.5/ES4/ES8 Anode Rod Inspection
Most hot water storage tanks manufactured and sold in the US, including the
Bosch models listed above, are made of steel. Steel when exposed to
water will rust and corrode; corrosion can be defined as the electrochemical eating
away of metal. To protect the hot water storage tank manufacturers employ two
levels of protection, a glass lining on the inner tank surface exposed to the water
and the insertion of a sacrificial anode rod.

Anode Rod InspectionTechnical Service Bulletin:
https://www.bosch-thermotechnology.us...