Yes, you do.
SOme customers contact us enquirng as to why they cannot lock the trigger on their gun into the 'open' position (i.e. with the machine running. This is not possible as such functions are not permitted for safety reasons, and there is legislation in place to prevent manufacturers from allowing this. If the gun held locked in the on position, and someone loses control of it with for example, a turbo nozzle in attached, there is a high chance of damage or injury ocuring to people, animals and property. 
All high-pressure guns have a child lock/safety function (marked above as Barnesikring) to prevent someone from using the gun in without unlocking it. This function should therefore only lock in the "off" position, and it is not possible to be used to lock then gun with the trigger in.
We have a gun called the Zero Force, this has a function that relieves pressure resistance in the trigger against the users hand, but still stops immediately when you release so that it meets all legislative requirements. It is easy to use and can be purchased from most AVA dealers or in our online store.
We are currently working on translating and rewriting all of our articles into English from the original Norwegian. Whilst we are proud of the quality of our language skills here at AVA, we are aware that there may be some slightly odd syntax and wording present in the articles that have been translated. The approach we have taken to this translation process is in order to get as much information as possible out to our customers in a timely fashion. Thusly the ongoing revision and updating of these articles by our British-Norwegian team will include slight changes to how the text is put together in order to bring it more into line with correct British English.