Hi,

This morning, our carrier natural gas furnace (20+ years old) which is an intermittent pilot system (at least, looks like those diagrams and goes tick tick tick with an ignition noise before starting up), decided to NOT start up.

The ignition was ticking, but the burners weren't coming on, and most importantly, the gas was still flowing! My parents happened to be visiting and sleeping in the basement, and noticed the gas smell quickly... once they are gone, I would not like this to recur and have even more risk of gas buildup in the basement.

My dad turned off the gas and the electric to the furnace immedately.

When the furnace tech came, he found that the furnace turned on with no problems, without any repairs. He said something to the effect of, since it was working when it came, he couldn't tell us what the problem was.

Any guesses out there? WEGS and WAGS welcome, I'm pretty worried and need to know if I should be more aggressive in pushing for a replacement part or a replacement furnace.

Thanks.

Cold be dirty spark electrode or a bad ground for the spark.

Thanks. The other thing is...

We were recently weather proofing. In the furnace room, the fresh air return was bringing in ridiculous amounts of cold air, and a previous tech said that since our house was so leaky anyway, we really didn't need the return to be open, and we could block it with a towel or something.

I never got around to that until a few weeks ago. Then, last week, my dad was puttering, and installed a door sweep on the basement door, blocking the 1cm gap there.

Is it possible that we made the room too air tight, and not enough combustible air was available?

Exact model of furnace?

Does it have a 3 wire pilot that looks like this?

Was the unlit gas at the pilot or main burners? I'm guessing the pilot. As previously suggested, the problem would result from insufficient or poorly targeted spark. In addition to other suggestions, try this: Pull the spark lead off the ignitor and the electrode, clip off about 1/4" from each end, and re-connect. This corrective action comes from a Carrier/Bryant service bulletin.

It may not be a bad thing to put a new furnace is as to it being 20 years old.New furnace will save you in gas and electric. If you go with a 90+ viribale speed motor. With the right install and furnace you get a good unit. Some units have 10 years part and labor..
Putting lots of cash in old furnace put it to new furnace... Not saying do not if old furnace but is it worth all the cash...