Abstract: Temperature controller apparatus for generating a control signal for supply to a control device which controls the temperature inside a chamber. The apparatus includes a plurality of input devices each receiving an indication of the temperature at a respective location in the chamber. Each of the received temperature indications is processed so as to form the control signal. In the event that any of the input devices fails to receive the respective temperature indication, output signals from such input devices are not utilized in forming the control signal. If all of the input devices fail to receive the respective temperature indications, the control signal is obtained from either previous control signals or previously stored control data.