I have a 18 year old high efficiency it shuts off intermittently sometimes requires a reset at the door switch. Also stops before its heating cycle has ended. It happends almost every night. Ill reset it it will be freezing in the house by morning. Unfortunately I don't have a lot of money at the moment I'm mechanically and electrically inclined. Any troubleshooting advice?

Work that's been done

New heat exchangers 2009
New heat blower 2008
New ignighter 2010
Clean filter installed

Also its prone to have ice build on intake due to poor pipe layout. I always make sure its free.