Complete 2 system furnace repair and preventative maintenance check. Check and find furnace inducer assembly pressure port clogged. Clear port and system operate. Check and find tankless hot water PVC pipe run into furnace double flue pipe and causing high moisture drain back into the furnace. Not code. Tankless PVC pipe need to run Separately. Cannot connect pvc with a metal pipe. Customers will call the company who install tankless water to address their problem. Need to replace inducer assembly and pressure switch.