Do I have a water heater problem or an electrical problem?

Question

I have a Rheem Marathon MR105245 hot water heater. Last night, it stopped working. I checked the breaker in the garage. It had not been tripped. I turned off the breaker to the water heater and took off the access panels to check the heating elements. Both heating elements measured 13.2 ohms. I turned on the breaker and checked for voltage at the water heater and there was nothing. There's an Eaton DPF221R fused disconnect above the water heater. The pullout wouldn't budge. I broke it to get it out. One fuse also broke. It looks like the plastic in the fuse box melted and the fuse that broke looks like it was heated. Should I replace the fused disconnect box and fuses and call it a day, or does this indicate a larger electrical problem or problem with the hot water tank?

Answer 1

Looks like the supply wiring at that disconnect overheated. Yet the wiring from the disconnect to the heater appears unscorched.

A common cause for localized overheating is loose connections leading to arcing. Whether a connection starts out too tight (which can cause plastic flow of the metal which leads to it being loose after a few cycles of use) or too loose, those that are not correctly torqued to specs tend to end up loose, and when loose they arc, which makes things hot.

So it might well be that a new disconnect, correctly torqued, will solve your problem for a long time.

When installing a new disconnect box, buy and install the cable clamp that is missing from this disconnect box where the 10/2 NM cable comes into it.