We have an ac/heating unit, honeywell c8600s, which will not turn on the heat. Power source is fine and when on FAN mode, air output turns on, but when switched over the AUTO, nothing happens. HELP! Please=-)

Note: some newer furnaces will not operate burner if the power polarity is reversed. Has there been recent electrical work in house? Experienced similar issue once. Check furnace circuit board for flashing error light.

Also, if nothing happens when placed on auto you should have course have a call for heat! (Set stat to temp higher than room temp). I'm sure you know this already.

You say the fan works, does the ac? What brand furnace?

Hello ivanh Thank you for your reply. We bought a $200 sensor, only to find that was not the problem. Now we are stuck with the new sensor and still have no heat. The thermostat has been set as you suggested. We recently, about three months ago, had a new tankless water heater installed... hmmm. We also had the Gas Company check all lines(gas heat)... the line is fine, gas is flowing freely... since we don't have a furnace circuit board(or do we? what does it look like?), what would you suggest next? Thanks again for your reply

I may be way off here but, can you see a flame(pilot light) in the furnace? More often than not, when a new gas appliance is installed(gas water heater) the gas is shut off and the gas pipes in the house get filled with air. Purging may be needed.

Hi, you are right about the pilot light. It is not coming on. However, we did get the lines checked out and they are flowing fine... any other thoughts? My guess would be the ignitor??

If you have a bad ignitor you will not see a red hot glow or hear a tick tick tick when attempting to fire.Replace glow plug or ignitor. Piloted furnaces are older units and must be lit by procedure on furnace panel. If you can not light pilot after following lighting instructions, U may have a bad thermal-coupler. Either way, it's a $20 part.

ivanh, Joshdta,
Exciting news! Figured it out!! Yippie! You got me thinking about the Thermal Couple... looked it up on YouTube... (lots of YouTube, actually). Then my husband and I went back to the furnace---opened it up... checked the thermostat... knew it couldn't have been the thermostat since the fan and the ac would actually respond to the temp changes... sooo, went back to the furnace! Everything seemed to b e working, but yesterday my husband actually had pulled the plug(computer plastic plug) which connects to what lookslike a mother board... we turned on the click to start the furnace without the plug being plugged into the mother board, then we reconnected it WHILE the clicker(maybe the ignitor button) was pushed down and guess what? Oila!! The furnace burners came on. We tested the whole procdure several times. Sooo, our conclusion: the plug is somehow not sending a message to kick off the burners... by unplugging it, we bypassed the wire which sends a message to kick on the burners... I am sure we will have to get the plug replaced(a plastic connector to the mother board)! Has anybody experienced something like this before? At any rate, thanks a million for your help. It inspired me to keep on before calling someone. We live in a small town and there seems to be a consensus to rip folks off due to lack of knowledge. Thank you also, Joshdta!! I love this site!! Just the other day, I completely replace my bathroom faucet(sink included) by myself--ahmm, I am not very mechanically inclined, but determined to get something done if I think I can...