The teacher is not paying attention to her work. She might be worried about how much she will have to pay plumber to get the boiler fixed. That's why she is probably distracted by the plumber. That's the person who is repairing the boiler. A boiler is a system that heats the water in the house. The boiler is in the basement of the house. It's down the stairs. That's why the plumber is downstairs.