Hi my name is Omar and am having a problem w/our furnace.It's a package unit, natural gas and is 20+ yrs old When I turn it on(heat) I can hear the thermostat click but nothing turns on(burners or fan, but when I turn on the AC the fan turns on). I opened up the side panel where the gas valve and burners are and noticed the pilot is out (also I noticed some build up on thermocouple and pilot, it looks like mildew? I'm not sure if this is a concern), is this supposed to be out? I hope this is a common problem and someone could help

All problems a common at one point or the other. There should be a wiring diagram on the back side of the blower door that can help you track down the problem.

You ned to find out if you have spark ignition or another type. Then you need to find out why it is not activating upon a call for heat

Since the unit is 20 years old the gas valve brand and part number along with the controler/spark box brand and model number will be a help since I do not have a listing on your unit.

Does the glow coil or sparker try to light the furnace?

Is there power going to the spark box?

Thanks for your response, hvac. I'll get the information on the parts when I get home(at work), but am wondering where is the spark box located? I only saw a transformer, fan limt switch, gas valve, thermocouple and pilot... I didn't know there was a diagram on the back cover, but like I said I'll get you the info when I get home... thanks again

It is possible there is no spark unit. It could just be a old fashion thermocouple safety design that you have to lite the pilot with a match.

Sometimes the pilot orifice will get plugged up and it will have to be taken apart carefully and cleaned. If the nut is hard to turn spray with WD-40 or you will twist the aluminum tube and be buying a new one. The pilot orifice is VERY SMALL. DO NOT jam something bigger in the hole or you will need a new orifice also. A very small strand of wire should fit the hole but if not find something small to fit the hole so as not to cause damage.

I'm starting to understand, if the pilot is not lit the thermocouple doesn't heat up and the gas valve won't open, right? But would the blower not turn on also?

When the furnace gets hot a control tells the blower to come on. If this is the main air blower that is.

Cleaned out the pilot and everything is working great... thanks a bunch :) you were a great help