When initially switching on, be sure to leave one steam arm open slightly to prevent an internal vacuum forming through temperature change.
Has the machine had enough time to warm up and fill up? After being switched on this takes approximately 30minutes.
Ensure that the isolation tap on the water feed pipe to the machine is in the ‘open’ position.
If hot water of team has been run off continuously to the extent that the boiler is empty, it may take a few minutes to ‘recharge’ ready for use again. Particularly applicable to machines with smaller boilers.