Electric liquid heater

摘要

A heater (10) for a liquid, comprises an elongate chamber (11) having an inlet and an outlet at opposite ends for the passage of a said liquid through the chamber (11), and electric heating means (15, 16 and 17) located in and along the chamber (11) for heating a said liquid passing through the chamber (11). The heating elements (15, 16, 17) are selectively energisable to provide different amounts of heating. The heater (10) further comprises first pressure sensing means (29) for sensing when the pressure of liquid being fed to the chamber (11) falls below a first predetermined value, second pressure sensing means (30) for sensing when the pressure of liquid in the chamber (11) rises above a second predetermined value, and electrical switching means (42, 43) responsive respectively to the first and second pressure sensing means to de-activate the heating means (15, 16 and 17) when the pressure of liquid being fed to the chamber (11) falls below the first predetermined value or when the pressure of liquid in the chamber (11) rises above the second predetermined value, e.g. when a valve 50 remains closed.