Gas and Oil Home Heating Furnaces - furnace wont come on

i'll do the best i can with the info i have. im not at my house right now so i dont have specific information on my furnace system. it is, however about 11 years old. it is a gas furnace. the house is a 4 bed, 2.5 ba multi-level in denver metro area. furnace is located in the partial basement. i just cant recall the make. it has a flameless pilot light. is that a "hot plate?" or "hot shoe?" anyway, it has been acting like this last year and now this year. the trouble is: when i set the thermostat high enuf that it should kick on, it often times doesnt. the pilot plate glows brightly, but then will often just shut off without igniting the gas. however, there are times when the gas ignites and it works. however, then it usually runs a cycle or two and then wont come on again. i had an older digital thermostat. i replace it last month with a new one hoping that was the problem. it apparently wasnt. i left the house for few days and when i returned it was forty some degrees inside. usually i have to keep turning the switch on the thermostat from "off" to "heat," hearing the furnace click on downstairs...then i go down to see if it lights the gas. if it doesnt i do it again, and usually...eventually it will light the gas. please help. i would like to fix this myself if i can. im pretty handy so im hoping i can save some money and not have to call a repairman. thanks a bunch in advance guys for your help.
brian

It could be a number of things..

-Pressure switch not closing
-Flame rod needs to be cleaned.
-Unit that don't have flame rod, it used the HSI (hot surface ignitor) as a flame sensor.
-Igniton control board may be bad.


I would check the vent pipes going outside to make sure they are clear.

Then if you got a flame sensor, it may need to be cleaned.