Trane Gas Furnance
The light may be your problem as Mr. K stated or if your furnace is fairly new and has an electronic ignition, it also has a computer card which sequences the start-up procedure. Believe it or not, these computer cards are sensitive to moisture. Hence, when the temperature drops, condensation forms. If your furnace is in an area where this can occur, moisture may be affecting the chip. In which case it needs to be replaced. Do not do this yourself. If your furnace is under warranty, Trane will replace the card. This is only one possibility. Furnace systems, especially the new ones can be fickle little buggers. You didn't say if your serviceman checked this avenue. If he didn't, find another, preferrably one with Trane training.
Good Luck, Len
I repeat what I've stated. Since your furnace is in a converted garage, moisture may be the problem. However the computer card may have failed. When your thermostat tells the furnace it wants heat, the card will activate the fan, then once the fan has worked for about 30 seconds to one minute the card will tell the ignitor to function. When the ignitor reaches the correct combustion temperature, the gas solenoid valve will open, allowing gas to enter the combustion chamber. Once the gas is burning, the fan will activate again to whisk away the CO2 waste gas. This process is all done in an irreversable sequence. If the sequence does not follow the numbers, the system will automatically shut down. Turning up your thermostat may activate the furnace, but that tells me the problem may well be in the card. Again, contact a Trane rep and your problem should be solved.
P.S. Your computer card may have a crack in it, causing intermittant operation, and again moisture WILL be a contributing factor.
If it is indeed the computer board, it should run around $50.00 or so plus installation. However, I strongly suggest you contact a Trane Rep and let them check out your problem. They make the furnace, so it is they who should know the most about it. From long experience with this type of problem, I can tell you that throwing money at it will only cost more in the long run. If I were in front of your furnace I could give you a definite answer. But I can,t do it long distance, I can only surmise from experience as to what the nature of the problem is.
Good Luck, Len
Just wanted to update you all on how things are going. We were able to get the furnance fixed, but only after some trying times. Had a Trane service tech come out and take a look at it. It turned out to be the limit (internal thermostat) that was causing the problem. It would shut the system down so often that it would cause the furnance to go into lock-out mode. While the tech replaced the limit, he forgot to change the voltage seting and ended up blowing the computer board. So we got that replaced for free. But anyways we have a furnance that works great. Also, refer to message "converted garage", he also susgested that we get rid of the allergy filter and change back to a paper filter. This is allowing a better air flow from the vents and is heating the house more evenly now. Thanks for all your help. Look forward to working with you all in the future. Hopefully just not about my furnance.