Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 04-04-2012, 05:53 PM   #1
Newbie
 
Join Date: Apr 2012
Posts: 6
Share |
Default

Pilot is ON, Furnace won't fire


Hi All..

So I have an older model natural gas Lennox Furnace which stopped working. The pilot light would not stay lit so I replaced the thermocouple. Now the pilot light stays lit but the furnace won't fire up/light. I switched the knob from pilot to ON, the gas line and furnace switch are on and the heat on the thermostat is turned up. The blower just blows cold air and I smell a faint trace of gas. Am I missing something? Or could it be a faulty gas valve? Any help is appreciated.

Kevin

Kewilliam is offline   Reply With Quote
Old 04-04-2012, 06:40 PM   #2
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,491
Default

Pilot is ON, Furnace won't fire


Age & model of furnace? First four digets of serial no.?

I am assuming that you have an older style lennox with a preheater in the fan/limit control that is now turning on the fan with a call for heat?
You shouldn't be smelling gas except for just a short while during the pilot relighting process.

Check if you are getting 24V to the gas valve?
Turn off the thermostat and jumper the thermostat connections on the gas valve (often marked TH as opposed to those marked TR that you would meter for the 24V test. If the valve doesn't fire...Change it.
Let us know what you find.

how is offline   Reply With Quote
Old 04-05-2012, 09:39 AM   #3
Newbie
 
Join Date: Apr 2012
Posts: 6
Default

Pilot is ON, Furnace won't fire


First four numbers of the serial are 4691
Model #GS18Q4/5-140-8 from 1991 (I think)

I'm not exactly sure where the gas valve is and I don't know how to check to see if I'm getting 24V to the valve. I'm a newbie to all this so if you could "dummy" down your comments/help that would be appreciated!

Thanks!
Kewilliam is offline   Reply With Quote
Old 04-05-2012, 10:40 AM   #4
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,491
Default

Pilot is ON, Furnace won't fire


Your furnace is younger than I imagined.

Furnaces will often turn on the fan and prevent the main gas valve from operating from blown internal fuses, tripping safety limits, roll out switches or pressure switch controls.

The gas valve is the same control that the thermocouple was attached to.

Considering your last post, a few photos of your furnace with the doors off would help us direct you.

Last edited by how; 04-05-2012 at 10:48 AM.
how is offline   Reply With Quote
Old 04-05-2012, 02:13 PM   #5
Newbie
 
Join Date: Apr 2012
Posts: 6
Default

Pilot is ON, Furnace won't fire


Here are some pics..

http://kfurnace.shutterfly.com/pictures#n_5

Last edited by Kewilliam; 04-05-2012 at 02:18 PM.
Kewilliam is offline   Reply With Quote
Old 04-05-2012, 02:33 PM   #6
Newbie
 
Join Date: Apr 2012
Location: Manitoulin Island Ontario Canada
Posts: 10
Default

Pilot is ON, Furnace won't fire


I'm not a gas man but the gas line from the valve to the burner shouldn't have a kink in it. I'd replace that first before trying any more trouble shooting. Can probably get a piece of steel line at a hardware store or Canadian (now Chinese) Tire. If it works check joints for leakage with soapy water. If you don't have a small pipe bender and/or flaring tool.....go to a local garage and ask them to duplicate the pipe...might do it for free or a couple of bucks.

Last edited by 43harley45; 04-05-2012 at 02:35 PM. Reason: forgot to add for leaking
43harley45 is offline   Reply With Quote
Old 04-05-2012, 05:17 PM   #7
Member
 
Join Date: Oct 2011
Location: pa
Posts: 4,325
Default

Pilot is ON, Furnace won't fire


Quote:
Originally Posted by Kewilliam View Post
this is just a standard gas valve..valve is set to pilot in picture...needs turned to on position...also as mentioned pilot tube is kinked...need to replace or repair this.....may need to trace out 24 volt circuit to see if a safty switch is open....
ben's plumbing is offline   Reply With Quote
Old 04-05-2012, 05:54 PM   #8
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,491
Default

Pilot is ON, Furnace won't fire


Whoaa!
That's one nasty pilot tube kink. In my neck of the woods, thats what gas supply tech's do to pilot tubes when they think a red tag is likely to be ignored. It looks like you have enough spare tube to cut out the kink and reposition it with a new pilot tube fitting for the gas valve.

Hope that the real problem was just the gas valve position even though you said it was turned back to "ON" (unlike what the pic's show).

Your lennox pic looks like a horizontal so you might actually have an older style fan/limit control with that preheater that is turning on the fan 30 - 80 seconds after gas valve gets 24V. If the gas valve gets left in the pilot position, the fan will still come on even if the heat doesn't.
how is offline   Reply With Quote
Old 04-06-2012, 08:08 AM   #9
Newbie
 
Join Date: Apr 2012
Posts: 22
Default

Pilot is ON, Furnace won't fire


Quote:
Originally Posted by 43harley45 View Post
I'm not a gas man but the gas line from the valve to the burner shouldn't have a kink in it. I'd replace that first before trying any more trouble shooting. Can probably get a piece of steel line at a hardware store or Canadian (now Chinese) Tire. If it works check joints for leakage with soapy water. If you don't have a small pipe bender and/or flaring tool.....go to a local garage and ask them to duplicate the pipe...might do it for free or a couple of bucks.
NO, NO, NO, NO! Use 1/4" aluminum tubing with an alloy brass compression fitting available from any heating contractor. Steel does not belong in any gas line of this type, it is reactive and will corrode. Actually, cut that kink out leaving about 1/2" on either side of the kink, take it to any good hardware store or auto parts store and get a 1/4" brass compression union of the same size and repair the line being sure to seat the tubing all the way into the fitting. Don't overtighten it, just firmly tight using two wrenches and check with a soapy water solution and be sure to rinse and dry it afterwards. Yes, be sure the gas valve knob is set to ON.
GarryE is offline   Reply With Quote
The Following User Says Thank You to GarryE For This Useful Post:
43harley45 (04-09-2012)
Old 04-07-2012, 04:51 PM   #10
REP
Member
 
Join Date: Jul 2011
Posts: 615
Default

Pilot is ON, Furnace won't fire


Once you replace that 1/4" alum pilot tube,Then you can turn the gas cock to the on position.That is that little valve lower left in the picture with the red knob.
REP is offline   Reply With Quote
Old 04-08-2012, 04:21 AM   #11
An old Tradesmen
 
Join Date: Oct 2008
Location: PA
Posts: 25,055
Default

Pilot is ON, Furnace won't fire


Wonder if someone tried to clean the pilot. Ended up losing the pilot orifice, and then kinked the pilot line to try and control the pilot flame.
beenthere is offline   Reply With Quote
The Following User Says Thank You to beenthere For This Useful Post:
ben's plumbing (04-09-2012)
Old 04-08-2012, 12:18 PM   #12
how
Member
 
Join Date: Feb 2011
Location: Vancouver BC
Posts: 1,491
Default

Pilot is ON, Furnace won't fire


One of my first service jobs was a simple tune up to a furnace that was apparently doing well. After I finished my servicing, the furnace started over heating and I can't figure out what I did wrong. The op came downstairs after I spent 30 minutes longer than I stated it would take. He just reached over my shoulder and turned the knob on the gas valve half way from "on" to pilot.

Said he'd had it adjusted that way for years ever since he eliminated much of the ducting. That first day was a rude awakening to just how far the ideal & the actual might be in the field.
how is offline   Reply With Quote
The Following User Says Thank You to how For This Useful Post:
ben's plumbing (04-08-2012)
Old 04-09-2012, 09:11 AM   #13
Newbie
 
Join Date: Apr 2012
Posts: 6
Default

Pilot is ON, Furnace won't fire


OK I'll work on replacing the alum pilot tube. One question..would the kink in the tube prevent the whole system from firing up?

Still trying to figure out why the pilot light won't fire it up?

Thanks for all the help!

Kevin
Kewilliam is offline   Reply With Quote
Old 04-09-2012, 10:33 AM   #14
Newbie
 
Join Date: Apr 2012
Location: Manitoulin Island Ontario Canada
Posts: 10
Default

Pilot is ON, Furnace won't fire


Quote:
Originally Posted by REP View Post
Once you replace that 1/4" alum pilot tube,Then you can turn the gas cock to the on position.That is that little valve lower left in the picture with the red knob.
Kewilliam ....... You forgot to read this part.
43harley45 is offline   Reply With Quote
Old 04-09-2012, 10:41 AM   #15
Newbie
 
Join Date: Apr 2012
Posts: 6
Default

Pilot is ON, Furnace won't fire


The red valve in the lower left of the picture is the main gas valve. The pilot light won't light without that turned on. My pilot WILL light and stay lit - it just won't catch fire to the entire furnace (not sure what exactly to call this). Make sense?

Kewilliam is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Bryant 394J Furnace - Pilot stays ON all the time Davexxx HVAC 17 04-08-2012 06:46 PM
Furnace pilot light will not ignite - Carrier 58 GS Furnace? rasilun HVAC 3 10-29-2011 09:38 PM
Fixed pilot light, now furnace or AC won't turn on mjcfromct HVAC 2 10-17-2011 10:46 PM
Bubbling Toilet, Pilot Light in furnace out, extremely sick SewerBreath Plumbing 24 05-09-2011 06:38 PM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.