[net.consumers] Pilot light out? A brief tutorial in gas heater service

brian@sdcc3.UUCP (Brian Kantor) (03/03/85)

> My heater hasn't been working all week. I finally looked at it
> and discovered the pilot light was out. Lighting it restored
> normal function.
> 1) How could this happen? Would a power failure have anything to
> do with it?
> 2) How did it know the pilot was out?

1. ``How did it happen?'' - lots of ways.  If the other pilot lights in your
house (if you have any others) were also out, then there may have been
an interruption in the gas supply.  A slammed door, a freak gust of
wind, a sonic boom, or other large air disturbance can blow out the
pilot too.  A less common cause is to have a speck of dirt in the gas
supply itself momentarily clog the ports or orifice in the pilot burner.

2. ``How did it know that the pilot was out?''  If your furnace is like
those I've seen, there is a metal rod sticking into the pilot
flame.  This is a thermopile (several thermocouples in series) which
generates a small voltage from the heat of the flame.  It activates an
electromagnet that holds the gas valve open - usually there is a thin
copper tube coming from the thermopile and going to the safety valve -
where there is a red button, or ring, or lever, or something that you
have to reset after the pilot blew out.  This widget shuts off the gas
if the pilot should blow out for some reason.

Troubleshooting the mess:  if your pilot blows out and you can't get it
to stay lit, look for crud in/on the end of the burner.  Carefully
cleaning it may help, if you can get to it.  If you get a normal sized
(yes, you should remember what size the pilot flame normally is) pilot
flame of the normal blueish color, that probably isn't the problem.

Look then to the safety thermocouple.  If you can light the pilot but
the safety valve won't stay open after about 30 seconds of heating the
thermopile (sometimes called the 'generator'), you can unscrew the
electrical connection from the safety valve and check with a voltmeter 
to see if the thing is no longer generating juice.

If the flame is clean and there is voltage coming out of the
thermocouple, you may have a bad valve.  Have your gas company or
furnace contractor take it from here - unless you are brave and skilled.

If your problem is that the furnace blows out the pilot light when it
lights off the big burners, you may have a clogged (flame smaller than 
normal?) pilot burner, or the gas pressure changed (bad regulator?) or 
maybe the main burner has become corroded or cracked.  Again, have the 
GasCo check it out for you.

I've fixed my furnace a number of times (and gas stoves, ovens, and pool
heaters too), but I'm not a professional.  So temper this advice with
your own common sense and an evaluation of your own skills.

	Brian Kantor	UC San Diego

	decvax\ 	brian@ucsd.arpa
	akgua  >---  sdcsvax  --- brian
	ucbvax/		Kantor@Nosc 

``Good Advice costs nothing, and its worth the price.''

jpexg@mit-hermes.ARPA (John Purbrick) (03/08/85)

 > My heater hasn't been working all week. I finally looked at it
 > and discovered the pilot light was out. Lighting it restored
 > normal function.
 > 1) How could this happen? Would a power failure have anything to
 > do with it?
 > 2) How did it know the pilot was out?

I had the pilot on my furnace go out a few months back, but it worked as long
as the red bypass button was held down. Diagnosis, bad thermocouple. The man
at the hardware store said sure, the thermocouple gets eroded by being in
the pilot flame all the time and a reasonable lifetime is 7 years. The
replacement cost $4.50 and took 5 minutes to install. Note that the tube
connecting the ends of the thermocouple unit comes in various lengths--get
the right one!