Abstract: An ink jet printer ink circuit (10) has an ink feed (18), an ink return (20), a pump (22) and a print head (24), the print head having ink inlet (26) and outlet (28) ports and ink jetting nozzles (30). When printing at normal levels of ink demand, the pump (22) causes ink to flow from the ink feed (18) into the print head (24) through the ink inlet port (26), and out of the print head (24) through the ink outlet port (28) to the ink return (20). The ink circuit (10) has print head ink supply boost means (22. 23) operable, when printing at high levels of ink demand, to cause ink to flow into the print head (24) through the ink outlet port (28) at the same time as ink flows into the print head (24) through the ink inlet port (26). Also a printer including such an ink circuit and a method of boosting a print head ink supply in such an ink circuit.