To heat a flowing liquid, an apparatus includes a heater block assembly having a heater block made of thermally conductive material. The heater block assembly has a tube inlet, a tube outlet, and a tube path between the tube inlet and tube outlet. Tubing extends through the tube path from the tube inlet to the tube outlet. The tubing is in thermal communication with the heater block. A heater cartridge, in thermal communication with the heater block, is configured to provide heat to the heater block for transfer to liquid flowing through the tubing between the tube inlet and the tube outlet of the heater block assembly. Circuitry is in electrical communication with the heater cartridge to control a temperature of the heater block by controlling operation of the heater cartridge.