Water heater zinc electrode

[mollerus]

I recently pulled out my water heater to install a bypass valve for the winter and reseal the door opening.  I noted some white powdery material on the back near the zinc anode hex nut.  When I pulled the zinc out for inspection, a feat requiring an impact wrench,  ALL of the ¾” x 12” zinc was gone and only the 1/8” support rod remained! This amazed me since the unit is electrically isolated  with plastic water and propane lines.  On closer inspection I found that the insulated covering on the 12v positive (hot) electrical lead to the step light had been worn through by compression between the heater and wood cabinet bracing after it comes through a hole in the floor.  The bare copper wire was in contact with the galvanized  case. I believe that the 12v potential on the heater case caused the less noble zinc to sacrifice itself as intended, but at a much faster rate. The powder I found was probably from the zinc in the galvanized case.  Now I am worried that the copper tubing in the heater or solder joints may have been weakened and the heater may need to be replaced.  The motto of my story is that your water heater zinc needs to be periodically inspected and replaced before it is gone.  I’ll bet that most heater zincs have never been inspected.  A $15.00 zinc is a lot cheaper than a new water heater.  Take a look at the routing of your step light wiring while you are at it.