Hi John,
1st. make sure external drain is screwed in. (white nylon slotted plug on outside)
Then make sure that COLD taps are shut. Open Hot tap(s) and the pump will now fill the boiler. When water flows freely from hot tap the boiler is ready to use. You can run it on electric and gas at the same time for a rapid heat up. Approx 20min to 70deg.
Make sure you drain down in case of frost and when not in use.
Unscrew exterior plug and open taps. Water will flow from drain point.
Hope this helps
Regards Jim