I have a 9 year old furnace that will not kick on. If we turn the thermostat on, the blower motor that vents the furnace out the side wall kicks on but the burners won't ignite. I looked through the view window and the flashing light indicated an igniter problem so I changed the igniter. Now, it still won't ignite. I can see tghe glow plug/igniter heat up but then it goes out. The light is on steady now (no flashing) so I have no idea what to check next. Any ideas? And, does the light that flashes the code automatically reset and if not, how do I reset this? By the way, it is a 100K BTU Intertherm furnace that uses LP. We were young when we buil, sub'd out the work we could not do ourselves and went with this furnace because of price. We have had nothing but problems, nothing major once they replaced the original furnace. But every year or so, we have a repair man in to fix it. I guess you could say we were young and dumb! Thanks for any input.
Egon,
Would that be the pressure switch or the vent safety switch? My manual for the furnace indicates there is a vent safety switch (manual rest) on the combustion air blower motor that vents the furnace out the wall, but I don't see an actual switch on this. And the motor does turn when the furnace is trying to come on.
It should have a pressure differencial switch that closes a set of contacts when the draft inducer motor is running,this switch will have a rubber hose running to it from somewhere around the condensate drain line.Make sure the rubber hose is clear...mine had ladybugs in it.............thats right ladybugs.......................................... .....................................
Thanks for the tip. I checked the hoses going to the pressure switch and when I blew on the hoses, I could hear a "click" in the pressure switch. The burners still won't light. I did check all the gas shut off valves and everything is on and the stove works fine. Still no code being flashed on the indicator light.
Check to see if the door to your furnace has an electrical schematic pasted to the inside. It'll show you what signals make up the gas valve permissives. It's usually a pretty simple set of permissives. As others have said, check the airflow/pressure switches, and gas pressure switch.
You said you had an error code that pointed to a bad igniter. I'd also check the glow plug thermocouple. Even though you replaced the glow plug and it's glowing red, if the thermocouple doesn't tell the controls that it's hot then the gas valve won't open.
One other thing. Usually the access panel on the furnace has a switch that must be made (panel must be in place) for the furnace to light off. So if you've got the door off and your watching the light off sequence to see what's going wrong, make sure you close the panel door switch.
To reset the controls on mine, I just cycle the power off to the furnace for a few seconds.
Take a voltmeter or ohmmeter and make sure the draft sensor is closing when the draft inducer fan is running...
Go outside the house and check the in and out pipes for the draft and make sure air is moving, you could have a wasp nest, or whatever blocking it ( or a small child could have packed it full of leaves for you =) or rolled a ball down it, or whatever, I need to screen my draft pipes ) ..if air won't flow thru it the draft sensor won't let the burner light...
You can take the ohmmeter and see which switch is keeping the burners from lighting, as others have said look at the schematic and see which switches are in the burner turn on circuit...
Thanks for the additional tips. I will cehck the schematics and put my meter on it. And, I will check my vent pipes for obstructions. I never gave that a thought and should have as we ran into a situation last year when my then 5 year-old hit the fan switch on our thermostat to "On". Couldn't figure out why the fan ran all day long and then my wife noticed the switch was "On". [img]/forums/images/icons/blush.gif[/img]
I am not very hand or mechanical, but I am trying to learn more. This site and tractorybynet have been very helpful to me.
When I got home, I went down and to see if it would fire up before I put my meter on it. It would go through the cycle, the combustion air blower motor (for the vent) would come on, the igniter/glow plug comes on, then I could hear the gas valve click, but it did not fire. I tried it again and when the glow plug lit up, I tapped the pipe going from the gas valve to the burner. This time when the gas valve clicked, the burner lit and the furnace acted normal. I assumed there may have been some dirt or something like that must have kept the line working.
The furnace was working fine until just a little bit ago. the burner would not light again. I went down and the light was flashing again, indicating an igniter problem.
Now what? I don't see a thermocouple in the manual. Could the thermocouple be the same thing as the "Flame Sensor" or "Burner Box Roll Out Switch"?
I may end up calling a repair man if I can't fix it myself in the next day or two. But I sure would feel like I accomplished something if I fix it. Of course, I would be helpless without all of you.
We are not totally without heat. We have a wood burner on the main floor of our home which pretty much heats the main part of the house. The bedrooms get a little cooler as they are on the opposite end of the house. Thanks.
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