Haven't had the problem but if it was mine I would check the fuses first then check that the wires didn't fall off the heater element then take off the wires and check the resistance between the connections of the heater element that is inside the water heater for electric operation. If there is NO resistance between the leads the element needs to be replaced.
Dick_B
2003 SunnyBrook 27FKS
2011 3/4 T Chevrolet Suburban
Equal-i-zer Hitch
One wife, two electric bikes (both Currie Tech Path+ models)