Okay here is the problem. I just moved into a new house but before signing the paperwork, I told them that the a/c and heater does not respond to the thermostat. They said that it needed a new ignitor. So they replaced it and it responded to the thermostat. I flipped it to "ON" and set target temps to 90 and 35, the heater and a/c both kicked on. Then I bought the house but now that its colder, I tried to turn on the heater. I click it to the "on" position on the thermostat and raised the temp to 90degrees. The thermostat clicked but the furnace did not kick on. Same with the A/C set thermostat to target 35degrees and still the furnace does not kick on. What do you think went wrong?

Is the "ON" position you refer to a heat/cool selection, or a fan selection? Brand/model# of furnace? Status LED present?

Fan selection. I do not know the brand/model# of furnace yet or the LED Status? Where do I find the LED status light. My furnace is in the attic.

Leave the fan selection on auto. And turn it to heat. Turn the temp up. If it does not come on. Go to the furnace and look at the bottom door for a small flashing light. This will give you the fault of what is wrong with the unit.

I checked the furnace, there is no flashing lights. I was staring at the circuit board, in the furnace but did not see any lights.

Brand/model# of furnace?This is important... any luck up there?

No luck, I see a switch up there, that saids "ON or "OFF" and its on "ON". Is there no power to the furnace if there is no light? I'm a rookie when it comes to electrical.

Didn`t see where you said you checked the breaker in power box to see that it was turned on or did you say if it was a gas or electric furnace,, let us know

I checked the breaker box and the switch seems to be on. What do you guys think it could be?

Nvm, I got it to work now. Turns out the door to the furnace was not securely closed all the way. At first I did not know but after pushing against the furnace door the furnace turned on and now everything is good. Also the safety cutoff switch next to the light switch was also turned off accidentally. Thanks to everyone for their advices.