Provided is test circuitry for testing a thermal actuator of a printhead nozzle arrangement of a printhead. The circuitry includes an open actuator test input, a column enable input and a row enable input. A drive transistor operatively links said thermal actuator to a power supply, and a bleed transistor is arranged in parallel with the thermal actuator. The circuitry also includes a sense transistor operatively linking an output of the drive transistor and inputs of the thermal actuator and bleed transistor to a sensing node, as well as a controller configured to deactivate the bleed and sense transistors and to activate the drive transistor when the column enable and row enable inputs are activated to link the thermal actuator to the power supply, and to activate the bleed and sense transistors when the open actuator test input is activated, so that the thermal actuator is short-circuited and the sense node is pulled high if the thermal actuator is open-circuit.