Unit: Lennox GCS16-411-100-1P Packaged rooftop

So the burner on this rooftop unit keeps cutting in and out when it first starts. I inspected the heat exchanger for any holes but didn't see any; although the style of heat exchanger makes it difficult to fully inspect.

As soon as the flame drops out the ignitor fires again and the burner lights so the flame sensor is working correctly. Voltage is continuous to the gas valve through all of this so its not the ignition module.

I put my manometer on the outlet of the gas valve but naturally I couldn't reproduce the problem at that point. The customer says the unit will run for a while and then lockout and then eventually come back on.

Im wondering if the flame is getting blown out by something (the building is on the shore of Lake Ontario and its been very bad weather lately) or if the gas valve is having trouble staying open despite proper voltage.

Hazard a guess.

Heres a link to a video of the problem. http://s38.beta.photobucket.com/user...e26ae.mp4.html