Today I looked at the unit marked number 8. Model gcs16-180-375-1 serial 5604F-01324. System will not fire in heat. I found the gas was shut off to the unit. I looked in previous invoices and found last year on dec. 2 it had the heat disabled due to a bad heat exchanger and kept tripping the roll out when the blower motor started. This will need a crane due to the size and weight of the heat exchanger. Sending info to Rick.