It is advisable to check with the manufacturer of your boiler for their specific recommendation. But usually, the first service of your boiler should be completed 12 months after installation in accordance with its warranty.
Following this, the boiler should be serviced on an annual basis moving forwards to make sure it is assisting your radiators and heated towel rails to perform to full capacity.
The BestHeating Guide to Buying a New Boiler includes further useful information.