Arrived on site to perform diagnostic on 8 year old York Furnace. Homeowner states that system is not heating properly. It cycles on numerous times and then it hit blows cool air. Cycled system for heat. System initiated the heating sequence, but cut off after the flame would ignite. It did this for about 5 tries and then went into lockout and turned on indoor blower. Pulled flame sensor and found it dirty, which was causing it not to read the flame. Cleaned sensor and put back in, cycled system and system came on Normally and started heating. Tested and verified safety components working accordingly. Checked ducting, found ductwork to be old and wrong fully designed. Went through findings and recommendations with homeowner. Homeowner is aware of the condition of her system and ductwork. Due to system being a heater only, homeowner wants to leave the ducting alone for a while until the system is replaced in the future. She does want the flame sensor replaced, I will be ordering flame s