Issue in Graphite Furnace

Hi, I have an issue in graphite furnace of novAA800D.

While running the temperature program, at the drying step, sometimes at pyrolysis step, the furnace temperature increases to its maximum (2450 °C) then at atomization step the furnace temperature does not increase which results in negative absorbance value. I have tried different temperature settings, also the cookbook furnace program, with and without modifiers but have the same issue. We also have tried temperature optimization for pyrolysis and atomize but observed the same abnormal behavior of the furnace.

Sometimes when the furnace temperature increases to its maximum(2450°C) at drying or pyrolysis step, the temperature holds for 15 to 20 seconds or more, which results in breakage of the graphite tube inside the furnace.

Sometimes the furnace works according to the furnace temperature program and we get good absorbance value but most of the time we face abnormal behavior of the furnace.

please a solution to problem.

thanking you