Keeprite furnace repair. Duct smoke alarm had tripped cutting power to furnace. Took apart duct smoke alarm and cleaned sensing tubes. Reassembled and powered system back up, no longer tripped and furnace is receiving power. Tested operation of furnace, working at this time Performed furnace maintenance while on site. Furnace filter was plugged. Overheating of the furnace could possibly have caused duct alarm to trip. Found no other problems or concerns with the furnace, it is now working safely and efficiently. Will have to return for fireplace maintenance.