Could it be this simple
I looked carefully at the panels and noticed that the one on top was not
covering the exhaust completely. I then noticed that they are
interchangeable. It’s possible that when I had the unit inspected before we
bought the house (I wasn’t here) they mixed up the panels. With the long
one on the bottom there isn’t nearly the gap for air intake as with the
short panel.
Hmmmm.
Derek