1. Inspect the thermostat at room temperature. If the valve is open, the thermostat must be replaced.
2. To check the valve opening temperature, suspend the thermostat in a container of water and raise the temperature of the water until the thermostat opens. The thermostat should start to open at 71°C +/- 5°C.
3. If the temperature at which thermostat opening takes place is incorrect, replace the thermostat.