Greetings from the Florida Panhandle
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Sometimes, the water heater contacts become intermittent. Try this. Open the outside water heater access door. There are four wires going into the main body of the water heater. Remove the one on your left, clean the contact, an replace it . Try the water heater again. If it still doesn't work, move the wire back and forth on the contact to help clean it. Try it again. Hopefully, this will work. Let us know if it works.
It's the wire closest to the shield with the two red wires going into it in the picture.
SuEllyn & Brian McCabe
WBCCI #3628 -- AIR #14872 -- TAC #FL-7
2015 FC 25' FB (Lucy) with HAHA
2005 Suburban 2500 Quadrasteer (Olivia) & 2011 Silverado 3500 (Fred) with Outfitter Truck Camper (Ethel)