Unfortunately it doesn’t look as though the problem is related to the system. You will need to contact your plumber to investigate. FYI if you have continuous problems then check to make sure that your outside tap is not connected to the header tank.
If it is it will be drawing more water from the header tank than the water going in and then causing an airlock. Your plumber should be able to fix the problem. They can of course contact us on 01733 405111 Option 2.