I have a Carrier 58 MVP variable capacity condensing gas furnace. It stopped working. I called the service person and he replace the Flame roll out switch. The furnace worked for 1/2 an hour or so and it quit again. I called the service person and told him that the flame roll out switched is tripped again. He said do not touch any thing I think your heat exchanger is cracked and need replacement. He has not done any tests to be sure that the heat exchanger is cracked. Are there any tests to determine that this problem is caused by faulty heat exchanger. The furnace is less than eight years old. Is there any thing else which could cause the flame roll over switch to trip? Your help will be very much appreciated. Thank you

Do you have the Infinity thermostat?

Air flow is another possibility. You can check static pressure with the Infinity Stat.

A combustion analyzer can easily determine if the heat exchanger is cracked. A cracked heat exchanger can introduce carbon monoxide into the home. Goggle carbon monoxide poisoning for more information.