PURPOSE: To actuate a temperature and pressure responsive valve member as a mutual valve seat and provide it with a cleaning function removing dust, etc., from the valve seat of a heat responsive member in a pressure and temperature relief valve for restricting the flow of a coolant in a water-cooled internal combustion engine.

CONSTITUTION: An inlet 38 and an outlet 64 of fluid are formed in a housing 32 and a fluid passage 18 including a valve seat 34 is formed by mutually connecting them together. A pressure responsive diaphragm valve 44 including an annular combination body of a valve member 46 and the valve seat moving to the valve seat 34 and moving to the outlet 64 according to the pressure of the fluid in the inlet 38 is arranged in the flow passage 18. A thermostat 82 including a movable valve member 50, a spring 72 for biasing the annular combination of the valve member 46 and valve seat in a seated position of the valve seat 34 and the valve member 50, and a second spring 86 for biasing the valve member 50 in the seated position of the annular combination body of the valve member 46 and the valve seat are arranged respectively.