Continuity mistake: Before Elmer puts pillows on the radiator in the businessman's room, there is a whistle on the radiator that wasn't there previously when Daffy discovers it was 'on the fritz'.
Continuity mistake: When Elmer runs back from the boiler room to the businessman's room, you can see that he has a bandage on his head, but when he runs from elevator to the room, the bandage disappears. It re-appears when Elmer is in the businessman's room.
Continuity mistake: When we see Elmer pressing the bell at the start of the cartoon, there is a book by the bell on the reception desk. When Elmer tells Daffy to take the businessman to Suite 666, the book has gone.