Boiler shutting down is indicative of heat not transfering to HW in HW mode. Eurocombi (I am sure) has cylindrical calorifier. With flowrate indicated, I would be looking for blockage on the primary side between the diverter and the inlet to the pump.
Is the plumbing plastic (if yes what is the colour of the pipes) or copper? What is water quality like when a radiator is vented.
Is the plumbing plastic (if yes what is the colour of the pipes) or copper? What is water quality like when a radiator is vented.