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Forum Index => Heating & Air Conditioning Repair (HVAC) => Topic started by: brad on October 23, 2010, 11:20:19 AM

Title: Furnance pilot trouble LENNOX GS 18Q3-75
Post by: brad on October 23, 2010, 11:20:19 AM
Pilot light would not stay on,so I changed the thermocoupler,lit the pilot held knob down, pilot came on and stayed on for about 6-8 minuets after I let pilot knob up and then went out.It would light again but would not stay on after letting knob up.So I changed thermocoupler again,lit pilot and after letting pilot knob up it stayed on again for a few minuets and went off,this time I heard a click before pilot whent off.It then would lite,but would not stay on anymore.What is wrong here?Can someone please help me out?
Title: Re: Furnance pilot trouble
Post by: JWWebster on October 23, 2010, 01:42:06 PM
Get a pencil eraser and take the thermocouple off the gas valve. Use the eraser to clean out that hole and reinstall the thermocouple. Use an old tooth brush to clean the mess off the pilot light. The flame of the pilot has to wash in the very tip of the thermocouple. If it washes through the middle their won't be enough electrical current produced to hold the spring loaded electro-magnet. If it still won't hold after all that then you need a new gas valve.
Title: Re: Furnance pilot trouble
Post by: brad on October 23, 2010, 05:07:11 PM
Thank you so much for the good info and things to do.I knew that I could count on you guys, you always come thru, thanks again.
Title: Re: Furnance pilot trouble
Post by: JWWebster on October 23, 2010, 05:18:36 PM
Did you get it goin yet?
Title: Re: Furnance pilot trouble
Post by: brad on October 24, 2010, 07:23:46 AM
I took pilot assembly out and cleaned it good and blew thru the gas tube and put it back in.It is still the same.Pilot will lite,but as soon as you let off of the knob it goes out.There is not a very good strong pilot flame.Maybe bad gas valve?? Is there a way to check gas valve.It is a honeywell VR800A 1012 model.
Title: Re: Furnance pilot trouble
Post by: JWWebster on October 24, 2010, 11:43:35 AM
Back in the day you could simply purchase a new safety magnet from RobertShaw. That however has been outlawed. You would need to replace the entire gas valve now. Does your gas valve thermocouple have 2 white wires coming out of the area where the thermocouple connection is? If so you may need to trace them wires down to a fuse that looks like this:
Title: Re: Furnance pilot trouble
Post by: brad on October 25, 2010, 03:40:02 PM
Ok back again with this thing.I finally got the pilot to stay on when you let go of the knob,but as soon as you turn knob from pilot to ON the pilot goes out.There are no white wires on the gas valve thermocoupler.The gas valve has two black wires and two yellow wires.One of the black wires goes from TH to gas valve body and one goes from TR to gas valve body.One yellow wire goes from TH to fan control box the other goes from TR to fan control box.On the side of fan control box there is a terminal strip that these wires go to,also the wires from thermostat go here.Now what? Help!!!!
Title: Re: Furnance pilot trouble
Post by: JWWebster on October 25, 2010, 04:07:51 PM
That sounds to me like a bad gas valve. Can you post pictures? The internet is so screwed up you cannot find anything out anymore. Look for a large flat blade screw on the valve. Remove the screw and under it is a smaller pilot adjustment screw. Try to up the pilot flame a bit till the thang stays on when you turn that knob.
Title: Re: Furnance pilot trouble
Post by: brad on October 25, 2010, 04:22:42 PM
Thank you,I'll go back and check.
Title: Re: Furnance pilot trouble
Post by: Icehouse on October 31, 2010, 06:45:08 PM
http://www.keatingofchicago.com/media/svcinst/TroubleGasValve021675.pdf
Title: Re: Furnance pilot trouble
Post by: JWWebster on October 31, 2010, 07:46:04 PM
Good picture Ice. See on top there is a wide screw or cap right next to the pilot line connection. Under that is the pilot adjustment screw.