He looked at it and said it was beyond repair. The furnace has a leak at the point of connection where the PVC Exhaust pipe connects to the top of the furnace. The leak is excessive. It's causing the top of the furnace to rust and it is also shutting the furnace off intermitently.
The repairman blew air through the condensate pipe and that did not cure the problem.
What could be the problem? Why would the furnace leak at the point of connection?