Could you please check once you did not assemble UV light or maybe just assemble one of two of your normal filter , and connect the water dispenser with water tap and see if the hot water water flow is normal or not ? Or maybe you fill water into the cold water tank , and see if the water dispenser work normally. From our engineer thinking , the hot water outlet not so normal and the reason can be 1. the water pressure maybe not big enough so the water in your filter not full or something in the filter or UV filter block . 2. Could you please check your UV lamp and change a new one for testing and see how is the result .