louie wrote:
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.

OK, you are probably right. If that was the case, I would assume that
the fire in both the boiler and the water heater should have been
extinguished.

- 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.

Thanks for the explanation of the role of thermocouple in keeping the
gas supply shut off when the flame was extinguished.

- 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.

There are two power switches for the boiler. One is in the basement
right next to the boiler, another one is right inside the entrance of
the side door that is the primary thruway in and out of my house.
Therefore, this is quite easy for the kid to toggling Off and On the
power switch without being detected when I am bending down putting on
the shoes for the kids. I don't know why we have a second power switch
near the side door. May be it is an emergency shutoff or something.

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.

Yes, you are right. The temperature in our area dropped significantly
in the evening when the flame of the boiler was extinguished; I am sure
there were high wind when there was cold front going through. And you
probably are on to something. But because we are in the heating
season, the boiler is on all the time (just a matter of high or low
flame). Even if the pilot light was blown off, the main flame should
not be blown off that easy right? And if the main flame was there, the
main flame should be able to re-ignite the pilot light (afterall, they
are right next to each other), right?

Anyway, I will go back home after work at around 5:00pm and check the
flame in the boiler to see if the main flame is ON or not. Normally,
the house should be quite warm at that time after a whole day sun shine
and a whole day of human activities inside the house. If the house is
warm enough for the main flame to go off, I should be able to observe
this at that time.

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.

Yes, you are right. I believe we should have the boiler inspected and
cleaned every year. Thanks for reminding me about this.

Jay Chan