On Tue, 5 Aug 2008 08:56:31 -0700 (PDT), cynic
wrote:

I've never yet found that failure mode!
Does the burner flange need a new seal or a wipe of fire cement?

I'm not quite sure what a boiler flange is. There is a hole (an
intentional one) on the front of the boiler that the blast tube,
nozzle, etc fit to. Is that the flange? If so, there did not seem to
be any smoke coming from there. The smoke definitely came from the
side at floor level.