The TRV is designed to protect the pump and operators in circumstances when the pump is running and the discharge outlets have been closed. In this situation, energy absorbed by the pump is converted into heat causing the pump water to heat up. When the pump water reaches a temperature of 42°C the standard TRV will start to open and will begin to discharge water at about 48°C. The discharge of hot water from the pump will allow cold water to enter, via the suction tube, thereby stabilising the overall temperature of the pump water. When the pump has cooled, the TRV will automatically close. A further version of the TRV available is rated at 74°C, and will discharge water at about 80°C. The higher temperature TRV may be necessary when the pump is to be used in very high ambient temperature countries. Here the static pump itself may be at a temperature higher than 48°C, which may result in the TRV being permanently open, causing priming problems. The hot water can be returned to the appliance tank or discharged to the ground. The latter option is preferable if foam is used in the system and avoids contaminating the tank with foam.