Concealed laufen wc doesn't flush - how do I fix it?

My concealed laufen doesn't flush. However, when I remove the air button and blow down it it does. Does that mean that the button isn't pushing enough air (it is pushing air), there is a whole in the bellows (doesn't seem to be), the syphon is stiff or something else. Any help and suggestion of where to get part gratefully welcome.
Many thanks