I’m not aware of a “bleed valve” for this… and if you are going to run the engine make sure that the header tank lid is open to allow the eascape of any air as well as being able to top us the mixture (remember the coolant / anti freeze!) – otherwise it will pressurise the system and potentially just create / move the air block.

    Another way of doing this without running the engine is to “pump” the top hose manually a few times and this should have the desired effect, again remember to open the header tank!