Why does my boiler gauge show no pressure?

The majority of modern boilers are installed as sealed systems with no header tank to automatically top up the system with water. The system pressure gauge, located either on the front of the boiler or on a nearby pressure vessel, will normally indicate 1 Bar when the system is cold. If your gauge is showing no pressure this would indicate that your system requires topping up. Why not ask your service engineer to demonstrate the procedure to you during your next visit?