Carrier furnace repair. Upon arrival system was cycling on pressure switch error. After performing diagnostics found condensate trap was clogged and heat exchanger was completely full of water. Drained excessive amounts of water, cleaned condensate trap and ensured rest of furnace drain was clear of blockages. Performed CO test, within range. Whie there are no signs currently of any damage to the heat exchanger, it is very likely all that water has taken some life expectancy off the heat exchanger Furnace was working consistently when leaving home, had run steadily since fixing clogged condensate trap. Customer noted loud metal banging sounds in ductwork when home is around 19-20 deg C, showed me video, sounds like a piece of metal hitting another piece. Inspected ductwork for dampers , found none. Advised customer to monitor situation and let us know if it returns Replaced leaking union for fireplace. Iron shaving was preventing old union from making proper seal