Italian to English Tech/Engineering Engineering (general)

I'm translating the troubleshooting section for an instruction manual for a pellet-fired stove where one of the alarms indicates "manutenzione ordinaria non eseguita correttamente: il crogiuolo non pulito o non posizionato correttamente, o il giro fumi non correttamente puliti ecc." I know that "giro fumi" can be translated as "flue gas pass" (or similar), but the reference here is to something physical that can be cleaned. Any ideas how to render the idea? Thanks in advance.