Welcome to the group. Try stirring the burnpot just before you raise the heat level. This might help remove some of the crud. If the control has feed trim rate try reducing the feed trim some. It should help burn the pellets a bit more. Or raise the combustion air trim. You might even need to open damper a little more. If all else fails, They do make a high ash burnpot liner for the Enviro stoves that will fit the GF55. You can find it under the Meridian parts listings.