Heating service claimed they checked my furnace and that the heat exchanger was cracked. They tried to sell me a new furnace. My wife says the worker did not even open his tools and certainly was not there long enough to have checked the heat exchanger. 
When I re-checked the furnace, It took 5 minutes to find the exhaust outlet clogged with coke from the exhaust pipe.I discussed this with the heating company and got no satisfaction. The credit collector got the same explanation and very clear pictures. they never replied to my picture evidence. But filed this none payment. This is abuse.