J F Graham wrote:... the feed door was apparently " settling in" and was not closing very tightly. As the gasket was apparently compressing to a point where there was very little resistance
My Harman Mk I did the same thing. I changed the gasket and within a couple weeks the new one compressed the same way. I concluded it was not a problem, as long as it was snug all around.
Does the fire itself look slow, or does it look normal? Are you using a different brand of coal? Just start a new pallet that might be different? Extreme percentage of fines in the coal that are restricting air flow? Is the weather suddenly much colder than it has been (it sure is here!) Is the circulator running constantly due to colder weather, where previously it was intermittent? I wonder if you have just reached the limit of how much heat the unit will produce? If you turn off the circulator temporarily will it come back up to temperature in a reasonable time?