The concept of 'putting into service' (mentioned, e.g. in Article 2 point 5 of Directive 2009/125, generally applies to products which are not 'placed on the market'. The aim of this concept is to identify the moment at which economic operators need to demonstrate compliance. It means the moment of first use within the Union. It concerns for example products which can be only used only after an assembly, an installation or other manipulation has been carried, such as boilers and water heaters, or products made for the manufacturer's own use.
Even if the reference to two terms may create the impression that 'placing on the market' and 'putting into service' are two different moments when a product compliance is to be assessed, this is not the case: as these two terms are mutually exclusive, either one or the other is relevant.
'Placing on the market' (making a product available for the first time on the EU market) and 'putting into service' (first use of a product for its intended purpose by an end-user in the EU) refer to two different 'modalities' in the process of bringing a product to the market; compliance is required only once based either on whether the product is placed on the market or whether it is put into service. Only where a product is 'not placed on the market' in the literal meaning, the moment of compliance is the putting into service.
Disclaimer: Please note that the European Commission cannot provide a legally binding interpretation of the EU legislation, as this is the sole competence of the European Court of Justice. Any remarks from the European Commission services are without prejudice to the position the Commission might take should related cases arise in a procedure before the Court of Justice.