I have a goodman central heating system model capf036a2a. The problem I'm having is when it turns on the flame will ignite and after about five seconds it will turn off. It will keep doing this over and over eventually it will stay on for a few days but it keeps doing this.

Clean the flame sense rod which should be in the pilot assembly with sand paper if you have it, and be careful NOT to break the ignitor. That should solve your problem

Check your thermocouple.

I had a very similar problem, when the outside temp dropped below about 15 degrees, my furnace would not come on. I replaced the thermocouple and it is working just fine now.

Good Luck!