RESISTIVE LIQUID HEATER

A liquid heater is described including a chamber for receiving a liquid, pairs of electrodes located within the chamber for applying electric current to the liquid, input terminals for connection to a power supply, a plurality of switches for connecting the pairs of electrodes to the input terminals, and a control unit for controlling the switches. The switches have a plurality of different states for selectively connecting pairs of electrodes to the input terminals in one of a plurality of electrode configurations, the electrodes having a different total electrical resistance in each electrode configuration. When switching between a first electrode configuration and a second electrode configuration having a second lower total electrical resistance, the control unit controls the switches such that switching between the electrode configurations occurs in response to zero-crossings in a voltage of the power supply or the electrodes of the second electrode configuration are energised with a voltage having a higher duty than the electrodes of the first electrode configuration.