Blow it with compressed air to see if it can be dredged. It is relatively simple to remove two pipes from the warm water pipe and blow them through the warm water tank.
You can also find a car wash, and then remove the inlet and outlet pipes of the warm air tank, and then wash them back and forth with the water gun of the car wash until the washed water becomes clear. If there is a special scale remover, you can also take off the antifreeze and use it with the scale remover, and then add a new coolant after use.