Make sure the intake it's not plugged. Sounds like you've cleaned the exhaust. The lights give an error code when it shuts down. Google that code. If its an outside intake it's had that happen when the wind blows strong directly into it. In that case I've taped it and used inside air. Another test is to unplug it and wire together the 2 wire that go to the vacuum sensor on the left side. This is temporary to test the sensor.if it works then you know the sensor is bad or you have a leak shutting it down, perhaps the gasket. For safety sake don't run it if it does work when bypassing that sensor. You can also do the same test bypassing the proof of fire switch. Also on the left side. You can Google those if you don't know where to find it. Good luck