This morning was the coldest day of the year in the Washington DC area
- a bone-chilling 21 degrees F. I stepped into my shower and lo and
behold - no hot water! I scurried to the basement, checked the main
circuit breaker and the water heater/deep well pump breaker and
everything was on - they did not trip.

I went to the water heater - a Bradford White Hydrojet that is less
than 3 years old - opened the upper panel, pushed the red reset button,
heard it click, and waited a few minutes. Later, I felt the copper tube
on top warming up again and when I checked the water faucets, the water
was starting to get warm. I had to leave for work so I didn't have a
chance to see if it would trip again. I'm now in the office for 3 hours
and the wife has not called, so I am assuming things are back to
normal.

I have done a fair amount of reading on the subject but, given the
relatively young age of this unit, I don't believe there is anything
wrong with the thermostats or the heating elements.

So my question is - is this just a fluke, an act of God, a one-time
random event that may never happen again? What could have caused it to
trip without the main breaker going off? Could the cold weather have
anything to do with it? What about the fact that our water source is a
deep well pump?

I guess I'm just looking for a rational explanation, so that I will
have peace of mind if the heater switch does not trip again.
Thanks for any insights, tips, comments, etc.