Came out today to perform one system HVAC service call. On arrival, customer stated that furnace kept kicking on and off. Upon inspection of the system found the heat exchanger to be cracked, the blower wheel was dirty, the flue pipe was leaking water, the Inducer port has buildup in, it the flame sensor had buildup and rust on it and reading weak. There was no AC on the house just a gas furnace in the bathroom closet. Upon finding the crack heat exchanger explained to customer that gas had to be shut off and the system needed to be replaced. Customer agreed to have a free estimate to replace the furnace. at this time system is shut off and gas valve is turned off.