I started up my Jotul GF 300 DV Allagash for its sixth season of light use and the flame was no more than a third of the usual height and all blue. The manual said that this may be due to too much air flow, and to reduce the airflow I should move the stud under the stove back. However it was already as far back as it would go. A serviceman came and spent two hours and was unable to make any improvement. Any ideas?