The vendor should provide a maintenance schedule, though the following can be assumed:
The ethylene glycol antifreeze is a consumable and will need replacing before its protection expires. Most UK OEMs use silicate-containing antifreeze with 2-year protection from new.
Seasonally inspect the boiler's flue hoses. Check that the hoses are still secured and undamaged, and that they're clear and unobstructed.
When in constant use, completely drain and refill the fresh water system once a month.
Safety and emissions tests should be carried out in accordance with local codes and regulations.