This furnace is about 14 yrs old I think and does not have an air conditioning unit; only heat. Started having issues with furnace not working some months ago. Has let us trip it on all this time by pushing all the reset buttons inside. Which reset button that makes it come back on has not had any consistent pattern. It will come back on but only will work for a few cycles of coming on and it repeats not working. The furnace starts the process and coil never fires nor flames appear inside. Replaced the sensor coil wire already and control panel is brand new. Neither stopped the issue. Now out of the blue the LED code 33 is coming on Control panel and none of the manuals explain these codes. What does that code indicate? Also where can I find the LED code list to keep with the manuals for the future?

Thought I best add that the LED code is now flashing 31. Also there is no list for the code explanation inside the furnace . Thanks everyone!