Quality control and certification of thermally modified timber (TMT) has undergone a number of changes after the product was introduced on the industrial market in the 1990’ies. But the standards and certification still leave a lot of questions, misunderstandings and faults to be resolved before it will provide a sound and true basis for product and quality assessment. The paper deals with these issues based on theoretical and practical experience by an equipment/process supplier (Moldrup-SSP) as well as plant operator. Even the latest versions of EN113-2 from 2020 and EN350 from 2016 have major flaws and fail to address the basic question of how to provide quality assessment and certification for durability based on the use areas of TMT. Treated product control as mostly excuted today may not offer a good picture of the quality of the finished product when bought by the final user and may result in disappointed expectations that will have an unnecessary negative impact on the product in the long term.