The actual worst time to have any amount of trouble with the furnace is during the Wintertide season.
If the ongoing trouble with your furnace happens during a Wintertide storm, then you are probably going to be in real awful shape.
My family and I have lived in the north Midwest for 60 years. Wintertide weather is never a surprise. I have seen blizzards dump 2 or 3 heavy feet of snow in less than an afternoon and I have seen chilly rain fall more like pellets of hail. Wintertide is never the time to have trouble with your central furnace. I can tell you this from experience, because I had a great deal of trouble with our furnace this winter. I had a respectfully timed tune up in September and the Heating and Air Conditioning specialist did not report that he could find any problems. Unfortunately, the people I was with and I did run directly into some trouble during a serious snow storm in February. I certainly have some comprehension of heating repairs and general furnace troubleshooting, but I could not repair the issue on our own and I was suddenly forced to call the heating supplier. Even though I called that shop early in the afternoon, I still had to pay a repair fee for same-day service. The local heating supplier did not repair our furnace until much later in the afternoon and, despite this, I still had to pay an additional $70 fee to have the job completed on the same afternoon. It’s a shame, they are the only venue in this part that will repair our equipment.