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!