You may think, it is as simple as just turning the breaker back on, or replacing a fuse, but you have to ask, why did the breaker trip? Sometimes old fuses just burn out, this is normal, and no big deal, (but please click here before you replace the fuse) but breakers don't trip for no reason. If it turns out it did not trip because of a problem with the water heater, CALL A LICENSED ELECTRICIAN. A leak inside the cover of the water heater could cause a short and trip the breaker. if your breaker is tripped, do not turn it back on before a full inspection of the water heater is done. Remember water and electricity don't mix.

Don't just replace the fuse.

As I said sometimes a fuse will just burn out, but if there is a short at the water heater, and you replace the fuse, it will pop in your hand. and scare the crap out of you, So for safety assume it burned out because of a problem with the water heater, do a full inspection of the water heater before replacing the fuse. If it turns out the fuse did not blow because of a problem with the water heater, replace it, if it blows again, call A LICENSED ELECTRICIAN. A leak inside the cover of the water heater could cause a short and blow the fuse. Remember water and electricity don't mix.