This is in a rental house and the tenant will have hot water and then it will quit. Every time, the high limit is tripped. I have replaced both elements, the upper thermostat, and even the old fuse box w/ a new breaker panel. After I put the thermostat in it seemed to be working fine - elements were heating independently. I guess I'll replace the lower thermostat but I'm not optimistic. Is there something esle that could cause this?