HVAC Questions? Ask an HVAC Expert for Answers ASAP
Hi, sorry you're having trouble with your furnace.
Have you had the front off of the furnace to watch the burners ignite?
It will ignite intermittently.
Have you tried cleaning the flame sensor?
After aprox. 10 seconds it will kick the system off.
where is that located?
I don't have a book on your exact furnace...are you near it? I can describe it for you.
I'll be there in 10 seconds.
You described a buzzing noise when it starts...that is probably the spark ignition..[you don't see a bright orange ignitor when it lights do you?]
No. There is a 1.5" diameter window that you can see the flame through.
Most of the time there is just a buzzing noise for about 10 seconds, then silence for the next few minutes.
Here is a pic of a typical flame sensor.
every once in a while the furnace will ignite without the blower engaging.
that will last aprox. 10 sec., then the whole cycle starts over again.
Ok..the buzzing is the spark ignitor. You should see a couple of wires going up to the compartment where the burners are...
there are 4 red wires
Are there screws holding a cover on the panel with the sight window?
the cover where the window is located has about 12 screws holding it on.
Ok..you''ll need to remove them to access the flame rod..
Here is what happens....
One end of the burner has the spark ignitor ...that lights it off...generally..at the other side of the burner compartment there will be a sensor or probe like the one I showed you...it senses the flame to make sure all of the burners have lit...
If it gets a little dirty or corroded..it won't sense properly and it will keep shutting your unit down. By recycling the power it resets the ignition module so it can try again.
You need to locate the sensor and clean it up with some fine sandpaper or steel wool.
You may see one with a bend in it like this one...a small single wire connected.
Not seeing it.
Im looking at the back of the burners.
It will be located in front of the burner nozzle where the flame comes out.
The flame actually has to contact it.
I am seeing a white wire going to the ignitor.
Ok...is there another wire anywhere in the direct area of the burners?
there are two red wires going into a small transistor looking part that is mounted above the burners, but it is not as long as the sensor that we had on our previous furnace.
That is a temperature limit switch..
this one is about the size of a dime in diameter, and aprox .5" long
No...we're looking for another probe that is directly in the path of the flame..
that's all i can see.
Ok,,,it could be part of the ignitor assembly...but not usually...
just one wire to the ignitor?
two red wires go to the ignitor
the other two are at the part I just described.
What about the white one?
one red going in is spliced into the white. i.e. it's the ignitor wire
does the ignitor look anything like this?
I'm familiar with the sensor from a previous furnace, but I don't see it here.
Could it be mounted about 1 foot above the burners?
no...it will be directly in front of the burner...
there are two red wires attached to a blackbox aprox 2X3"
that's what I thought.
Let me try to attach a photo.
That would help.... Sorry I don't have a breakdown of your furnace...
Crap, it wont let me upload.
has to be a url
Ok...no problem...I'm looking for some literature..
Tom, I uploaded to my website here http://thinairmedia.com/2010/10/28/furnace-problems/
ok...let me see if I can get there....
Hopefully this helps
Ok..2 reds are definately a temp limit..so we don't need to concern ourselves about those..
Did the ignitor look like the one in the last pic I posted?
A white porcelain base with a prong looking device?
It's possible, but it's facing away from me
Or does it look like 2 metal rods (electrodes) that would spark?
It looks like one porcelain
Ok...if you looked in that window while it's lighting do you see a really bright orange glow?
what's baffling me is that I can't find the temp sensor.
Ok...so no other wires...just the 2 reds and the 2 to the ignitor?
Can you pull the wires away from the rubber gasket on the left a little and make sure one isn't hiding below the others?
There are only 4 going in.
I just updated my site with a photo of the lower area.
Ok....hold on and i"ll check it..
I just added another.
the two red wires above the burner.
Ok....the two above are the high limit for the heat exchanger...
So...to answer 1 question...the ignitor does glow before the burners light?
I can't see it through the window, it's offset.
should I light the furnace with the access door off?
It would be bright enough to light up the entire burner box..
it won't light with the door off...
I'm not seeing anything orange prior to the burner lighting.
There is a pressure switch that looks at burner compartment air pressure and won't let it go with the door off anyway..
Ok...there is probably another justanswer.com tech itching to answer this because he's more familiar with your furnace....I think I should opt out and see if I can get you a better answer...I think there is another tech or two still online...
Sorry I wasn't more help....usually we can talk these things through...
what do I do now?
I'm going to opt out..that will open your question up to other techs...if someone is online that can answer they will reply to this thread just as I did. He will be able to see our entire conversation which will help...
Thanks..and I'll see if I can find someone for you... Tom