I have a gas central air/heat unit. When I turn the thermostat on and to heat the burners click on and force heat for about 5-10 seconds and then go off, then there is a click and they come on again for 5-10 seconds, then off, then click on for 5-10 seconds, off... This just repeats and the temperature inside does not go up. Also, the blower is running during this process its just that the burners do not stay on. Does anyone know what would cause this. A bad switch in the unit? A bad thermostat?
Any and all help is greatly appreciated.

Thanks

If burners do light, but quickly extinguish, the flame sensor may require cleaning.

Thanks for the reply KC13.
I have a Day & Night model# 36/100YAC-108C and when I open it up I do not see a flame sensor like the one in the attached images.
Thanks for all of your help.

I can't find ANYTHING on this unit. Can you post a few pics of the unit with the front panels removed?

Here you go.

Looks to me like unit needs a good cleaning and serviced by a pro,, he will find the problem and the flame senser

You have a White Rodgers safety system on your unit. That little black square box about about 1 inch by one inch with the wires attached is probably the culpret causing your problems. I agree with wmproop that it could use a good cleaning,It is a old furnace that should have the heat exchanger checked and the pilot safety control tested and if necessary replaced. Those controls can be wire wrong if you are not real careful so here is another reason to get a on site professional for the repair. Here is a pic of the control I am talking about. They make many different ones that look like this and the part number is on the control. Usually the part number of the one you actually need will be a new part number since most of the old ones numbers have changed.

Wow, a mercury-filled flame sensor. Good luck finding one if it's bad. You may have to convert to standing pilot, or replace the unit altogether. I'll do a li'l snoopin' around the old stock at the shop tomorrow...

Plenty of these on Ebay and they are still available at HVAC supply houses BUT there are a few different styles that can include one with a built in resistor so the exact part number of the old one will have to be transposed to the new control safety.

I found the part on eBay for $45 incl shipping. I got it today and installed it and I now have heat! Thanks to everyone who replied to my question for all of your help! I greatly appreciate it! Have a Merry Christmas!
Ken Saldate

Glad you got it going. The W/R system always worked well but the piece you replaced only lasts about 25 years or so but they sure do last longer than the newer type safety controls today.