Ovens, Irons, Fridges and other things have a gizmo called a Thermostat that controls the temperature - The thermostat is an on/off switch that changes at at a point set by the user. Sometimes they fail.
When the fail OPEN circuit nothing happens.
When they fail CLOSED circuit the cooling (or heating) carries on in an uncontrolled way.
You very probably have a defective thermostat.
Peccavi, October 2009