I have the following specific questions:


- Would this happen when the natural gas supply was momentarily
running out of gas? But the fire in my relatively new water heater was
still burning while the fire in the boiler was extinguished. If the
natural gas supply was momentarily stopped, I would assume that the
fire in both the boiler and the water heater would be extinguished,
right?

Yes, if your gas supply was interrupted, the boiler would shut off.
This is VERY unlikely and probably isn't your problem.


- Is the boiler smart enough to automatically switch off the gas
supply when it senses that the fire is extinguished? I am asking this
because the control switch was at the "ON" position but I didn't smell
any gas.

Yes, there is usually a thermocouple or sensor above the pilot flame
(in pilot ignited appliances like most older boilers and water
heaters). When that cools off, the gas supply is shut off. This is
why you need to hold the pilot button on many newer gas burners for a
few seconds after lighting to make sure the gas stays on while the
thermocouple heats up.


- Will this happen when someone (like my 2-year-old child) toggles
the power switch of the boiler Off and On?

It's possible, does your 2yo spend much time near the boiler? Having a
2yo myself, it's something I would strongly discourage, with locked
doors if necessary.

If I had to guess, I'd guess you experienced some unusually high winds
recently, as did a large portion of the USA. Occasionally, a wind that
is unusually high or from a different direction than you are used to
will cause a backdraft down the chimney that can actually blow out a
pilot flame just like blowing out a birthday candle. When the pilot
goes out, the thermocouple cools down, and shuts off the gas supply
until someone comes along and relights it.

You may want to have your chimney and boiler inspected. In addition to
occasionally blowing out the pilot flame, this can also force
combustion gases (like carbon monoxide) into the house instead of going
up the chimney like they're supposed to. An infrequent occurance may
be just due to unusually windy conditions, but having your system
checked out by a professional would be the smart thing to do.