We had a company in today to do an inspection on a 4 year old ICP furnace. They used a system that I am sure you are all familiar with called an injection test. They pulled off the flue pipe and plugged the inducer motor with a rag. Then the tech pulled off the side of the plenum lifted the coil and checked for leaks with a monitor. My question is this. If the monitor gives a positive reading does this insure that the heat exchanger is bad or could there be a problem with something else like gaskets at the inducer motor? Shouldn't the inducer motor be pulled and the ends of the heat exchanger tubes themselves be plugged to narrow down the problem?

Thanks in advance for your help

PS The readings were strongest at the front of the heat exchanger and and he was getting positive readings on all three tubes. Would this be a crack in each of the tubes?