I have a Weather King gas furnace. 90+. It purges. Igniter lights up. It even lights burner breifly or even sometimes till fan kicks on. I have checked hoses for water and the exhaust pipe has 2 elbows, but no low point to collect water. I have cleaned and even replaced the flame sensor. It generally just stops and then goes through the same process again. It was working fine and then started doing this and I blew air through the burner and cleaned the flame sensor and then it worked fine for about 3 days. Now it is doing it again and I can't seem to correct it.