Of course. The condensate has no-where to go. Many thanks again - I can rest easy now
PS>You advised me on installing a tune-up kit for the furnace, and I did, and it performed much better. The burner was nearly all gone! A short time later the motor started making noise so I replaced that too. Good thing, it hit -10c the other day and the furnace has gotten a big workout.
So you're two for two with me - if not more!