As mentioned previously in Steam Generator article under Complementary Equipment, ink used in the cartridges is subject to dry when it interacts with the air. In case, when the cartridge is kept unused for a long time, dried ink becomes solidified hardly. In this case, use of cleaning solution is required.
If clogging is not solved after the spraying of pressurized steam through the print head, then cleaning solution is used. After turning the cartridge upside down, one or two drops of cleaning solution is dropped on the print head. And the cartridge is kept for a while in this state. Usually, 1 hour waiting time is enough to solve the clogging.