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From: res@ihuxn.UUCP (Rich Strebendt)
Newsgroups: net.consumers
Subject: Re: pilot light out?
Message-ID: <986@ihuxn.UUCP>
Date: Wed, 6-Mar-85 18:43:33 EST
Article-I.D.: ihuxn.986
Posted: Wed Mar  6 18:43:33 1985
Date-Received: Fri, 8-Mar-85 03:12:42 EST
References: <767@amdcad.UUCP> <298@mtxinu.UUCP>
Distribution: net
Organization: AT&T Bell Laboratories
Lines: 27

> > 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.
> 
> > 2) How did it know the pilot was out?
> 
> There's a valve operated by the heat of the pilot.  If there's no
> pilot, then the valve closes and cuts off the entire gas supply.
> So far as I know, this is an entirely mechanical setup.

No.  There is an electrical solinoid that is operated by the
electricity generated by a thermocouple upon which the pilot light
impinges.  No pilot light => no heat on end of thermocouple => no
electricity being generated => solinoid drops out closing gas
supply valve.  The need to heat up the thermocouple to get enough
current to hold the solinoid in is the reason that you have to hold the
valve to the pilot light open for a while (typically about a minute)
after lighting the pilot light.

If you find the pilot light out repeatedly with no good explanation 
(like a contractor ripped out a gas main), then look at the possibility
that the thermocouple is dying.  It should be fairly inexpensive to
replace, and on an old unit may be the cause of the kind of problem you
may be having.

					Rich Strebendt
					...!ihnp4!ihuxn!res