I just repaired mine. It started tripping the ground fault circuit. I suspect its original (20 years old).
I replaced it with the Camco 11673
. I replaced the heater probe and the control sensor.
It doesn't replace the propane, it augments it. We would leave the electric on to keep the water hot (set at 120 degrees). But if we wanted to take a shower, we'd turn the propane on to boost the temperature more.