simmerstat

noun

An electrical control device which turns a heating element such as a stove hotplate or grill on and off in a fixed cycle. The control knob on the simmerstat determines what proportion is spent on, and what off. For example with the knob turned to a quarter it might use a cycle of 5 seconds on then 15 seconds off, thus giving roughly a quarter of the heating elements full power. [ not sure this link is fantastic