Furnace Problems - Blowing cold air - Please help

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.

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?

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.

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?

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.

Hi, Can't you think logic? Thermostat sends heat command signal(24V AC on W terminal) to furnace >>>> furnace gets the signal and actuate gas valve >> valve opens >> gas flows >> pilot ignites the gas >> so on and so on. Follow this logic flow and see where the trouble is. If it is over your head, call the pro.

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.

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.

Are you suggesting that his thermocouple is bad?

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?

I suggest that he call in someone that's qualified to work on gas furnaces, as it's painfully obvious that he's not.

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.

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?

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.

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?

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

Go crawl in a hole eddy, you're a f****ng dumbass. How's that for name calling asshole?

About what I'd expect. Your mamma is proud of you.

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,