I'll try to explain this as best as possible, hopeful someone can help me out.

I have an Armstrong oil forced air furnace. Recently it has started acting up intermittently. The t-stat calls for heat and sometimes the furnace will fire and other times it will not. I do always hear the click from the t-stat. I can successful jump the furnace on and it will fire and stay running every time. The furnace has never gone into lock out mode. The local hvac company said it was a faulty t-stat as they could find no issue on the "oil side". I replaced the t-stat and the wiring from the t-stat to the furnace, issue is still present.

What part do I replace next, I was thinking it may be this part but I'm no expert. I'm 99% certain the issue is not the t-stat or wire since I have replaced both.

Thank you for any advice or assistance. I can attempt to answer any questions that may be of help.