-It is not that critical to be level.
-The gas setting should not be less efficient than 12 or 240v.
-All three settings are just different ways of applying heat, thus causing pressure, to make the coolant do it's job.
-The problem with the gas setting is the flame has to send its heat up a tube which usually has a spiral deflector up the middle. This means that rust particles, dust and debris cannot fallout of the bottom of the tube.
To get at the tube you could try to remove the outside grills else you will have to remove the whole unit to get at the back of it. Bear in mind the gas jet may be partially blocked as well.
Cledlyn
August 2008