A switch having closed and open positions moves from one position to the other in response to either an elevated temperature or an excessive pressure. A switch member of bimetal material or shape memory alloy operates in response to an elevated temperature, and a foil diaphragm that cooperates with a bumper operates the switch member in response to elevated pressure. The diaphragm may rupture to vent excessive pressure in the event pressure continues to rise despite operation of the switch member or due to failure of the switch member to operate.