Performed heating maintenance Both Daikin modulating 97% efficient natural gas furnaces Replaced 20x25x4 filters Pulled flame sensors and cleaned Pulled condensate traps and flushed with hot water... both were full of gunk that would eventually stop the furnaces from operating Re-wired condensate safety switches to the alarm terminals on the furnace control board... this makes the system display an alarm on the thermostat rather than the stat going blank if there's a water backup in the drain line Repaired exhaust pipe leaks with primer and glue Disassembled and cleaned the heat exchanger core and filters on the aprilaire 8100 heat recovery ventilator Checked for signs of water leaks internal to the furnaces Blower wheels are OK All wiring is in good shape and connections are tight Furnaces are operating normally at this time