Poor suction can be caused by several factors, including a full dust container, dirty filters, blockages in the hose or brush roll, or a brush roll that is not spinning freely. To restore optimal suction, empty the dust container, clean and dry the filters, and remove any debris from the hose and brush roll. Also, ensure the brush roll is correctly refitted and spins freely, and check that all parts are securely assembled. Regular maintenance helps maintain strong suction and prolong the life of your vacuum.