Furnace Problems - Blowing cold air - Please help

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Hey guys,
I know nothing about how the furnace or heating work in general, but I will try to explain my problem and I hope someone will be able to help me out.
So here we go... I turned on the heating this morning, set it to like 25 degrees celsia, while outside was like 5 above zero and our gas Furnace (maker: Clare) seemed to go on, but after a little while I realized it is blowing only a cold air. So I went to basement and checked the furnace pilot. It was on and burning.
I thought maybe furnace needs to be reset, so I turned off furnace power switch, waited couple minutes, then turned it back on, but it's a same problem. Pilot is on, but that coil in the furnace where gas goes to burn never fires up.
Anyhow, so I checked our air filters and there was a lot of dust on it... and I mean a lot... so I cleaned it properly, put it back, but when I turned air filter box on, that little led light doesn't light up and I can't recall if it did before or not. But before I could always hear like little sparks from this air filter and now it seems completely dead.
I wonder if the air filter and the fact that it might be damaged could somehow affect the furnace itself.
Please tell me what else I can try. I am no longer sure what is going on. Not sure if I should call a furnace repair man, or electrician or if there is anything else I can try.
Joe
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On Oct 13, 1:10 pm, snipped-for-privacy@gmail.com wrote:

Maybe you just turned the fan on. Usually the blower on a furnace will not start until the burners have been ignited, unless of course you just turned on the fan on the T-stat. An air filter would not cause the burners not to ignite. If all else looks ok, then call a tech.
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Termostat fan was set to ON. I set the termostat to HEAT and FAN option to: AUTO.
Now it's not doing anything. Pilot on our furnace is burning, but burners are not ignited. What could be the reason for burners not igniting?
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Thermostat is in the proper position. The pilot is heating a thermocouple that says it is OK for the main gas valve to open. If the thermocouple is bad, the heat will not go on. It is a safety device to assure the gas valve does not open with no way of igniting the gas. They are generally cheap and can be found a good hardware stores and home centers.
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Thanks Edwin,
If I understand this right, the thermocouple is a sensor which senses if the pilot flame is hot enough to sustain burning the gasfuel from the burner, right? So if it's broken, the thermocouple keeps the main gas valve located in the pilot assembly closed and it shuts off the gas valve to the burners?
Hm, that makes sense and that is possibly a reason why my pilot is on, but burner is not.
Is it hard to replace? Where would it be located on this 20 year or gas furnace, brand: CLARE? Any idea? Should I do it myself or is there a way to just clean the thermocouple from dust or something like that to make it work?
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No, dirt is generally not an issue. At 20 years, a defective therocouple is quite reasonable. They are easy to install (screw-in deal), but considering your lack of familiarity with gas appliances, I'd call the gas company, or whoever services your burner. The other issue is making sure that you have the right size themocouple. Not a big deal, and 1/2 time, at most. It is also possible that you have a defective gas valve, or power is not getting to the electrical controls on the valve. Check fuses first, before you call, and that the breaker is Ok for that circuit.
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professorpaul wrote:

Hi, Commonly thermocouple's job is to supply small amount of gas to keep the pilot stay on. If it's bad pilot will go out.
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snipped-for-privacy@gmail.com wrote:

    On the ones I have seen, the thermocouple is used to control the pilot light. In other words, the pilot light will go out if the thermocouple does not sense the pilot light being on. Therefore it will NOT release gas to burn, OR to keep the pilot light lit. Yours may be different, but that is how the ones I have seen work.
    That would lead me to believe that the thermocouple is PROBABLY good since your pilot light stays lit. Check for 24V A/C across the coil of the gas valve when heat is being called for. No 24V, a problem with the wiring to, or the thermostat. If you have 24V, remove one lead and check for an open coil on the gas valve. It happens quite often.
    It goes without saying that your gas valve is set to the "ON" position and not on the "Pilot" position. Being in the pilot position would give you the symptoms you described. If you do not feel capable of making these checks, call a serviceman for the furnace. Electricity and gas are two things you should not mess with unless you are sure of what you are doing.

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Are you suggesting that his thermocouple is bad?
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It is a possibility Although the thermocouple is supposed to keep the pilot valve open, I've had it where the pilot would still light and the burner would not get the signal to open. Fixed our heater at work.
There are other possibilities. Gas valve, limit switch. May also be a solenoid sticking after sitting all summer. What do you suggest?
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generally
pilot
I suggest that he call in someone that's qualified to work on gas furnaces, as it's painfully obvious that he's not.
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wrote:

If the termocouple were bad then the pilot would not stay lit you frickin idiot. Stick to givivng advice about something you know cause heating isn't it.
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<old furnace dude> wrote in message

Best you can do is call names? I had a furnace problems and the pilot was lit, but the thermocouple was still the cause. Perhaps the voltage was low. I did not test it. It may not be common, but it was in my case. So, what do you propose as a solution or did you just come here to show you are a mean old bastard?
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low.
Try looking up the difference between a thermocouple and a thermopile. Then, the next time you try to help an OP, make sure you're familiar with their equipment.
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I had thought ( at least with most furnaces) that the blower will come on only after the burners ignite, so why is this blower coming on if the burners are not on?
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wrote:

Because the fan relay is bad or a limit switch is open. DUH!
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wrote:

Go crawl in a hole eddy, you're a fucking dumbass. How's that for name calling asshole?
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<old furnace dude> wrote in message

About what I'd expect. Your mamma is proud of you.
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I am having the exact problem with my Clare furnace. The first blower starts...then the pilot light ignites....then the main burner kicks on for only a second...then the main blower starts and it acts as if nothing is wrong. Even the small computer lights up like there is nothing wrong. Of course it only blows cold air and never shuts off because the t-stat never climbs.
Any help?
Thanks,
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Ok guys, so here is an update. And a quite a weird one.
I listened to your suggestions and checked the furnace and tried to figure this one out. I tried to see if it's dirty inside, and it is, dirty. Not entirely hideous, but 'hey' it's 20 years old and I doubt it was ever cleaned. I can't post the picture here, so just imagine, that the level of dirtiness inclines more to the negative side, if you know what I mean :)
So, it's not very clean, dust everywhere inside, but I doubt that it is less dirty than it was this March (when it was still running).
In my opinion this has nothing to do with how dirty it is.
Then I checked the electric box and as Edwin Pawlowski said in this thread, voltage is low. It's not enough, only 14volts... why? I've no clue, because I don't have much knowledge of the topic.
In the mean time, pilot is still working, everything else seems ok, except the burned never goes on. And that is probably caused by not enough voltage, thus gas valve is not opening.
Anyhow, so because I know sh*t about what to do, I called an electrician/furnace repair man.
This guy walks into our basement, kneels next to the furnace, doesn't do anything just looks at the burning pilot, shakes his head and says, that we should immediately turn it off, if we don't want to die. I am looking at him, trying to figure out, how the hell he could find the problem so quickly without checking anything. So I asked him if he could check the electric box and the voltage. He said, that gas valve is not controlled by it and we need to replace the whole unit immediately and if I don't have the money, I should get a loan or financing. I repeated if he can take a look at the box, that there is not enough voltage and that from my point of view, if there are going electric cables from the box to the valve box, it is probably controlling the valve.
This got him really upset, but he checked it and said, that there is a problem with the box, it has only 14volts :) So, I asked if the transformer is not working. He said: most probably not.
So, he was a bit shaking at this point and told me that it's old, dirty. That cleaning will cost me $600 and the new unit $2000. That he won't repair electric box, because even if it worked, he doesn't want to have anything to do with the fact it will kill us afterwards... and so on and on... wouldn't let me say one word.
When he eventually stopped, I asked if he can clearly tell what the problem is. He said: electric box and that it's dirty. I said: I will clean it up, you repair the box. He said: No, got pissed, closed the gas going to our furnace and left totally pissed. I was walking right behind him, asking: "And, how much do we owe you?" He replied: "Nothing, if something happens here and you died, cheque/ bill would be a proof I was here and they could put me to jail!
Ufff... so he gave me a scare at the point where he would accept any cash, until then he seems only like a regular asshole, trying to sell me a unit without even wanting to take a look at what the problem is.
Can someone tell me what my next step should be? Should I call another electrician and let him repair the transformer from 120 to 24volt and run the unit, or forget it and buy a new furnace?
I am kind of worried now, because of what he said and he is definitely a bigger expert than I am, but I have to think logically too...
What do you suggest?
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