Pressure relief valve used to alleviate pressure damage to pressurised fluid systems, such as in calorifiers. The relief valve is set at a predetermined level that will divert some of the fluid away when the pressure in the system reaches that point. This is to stop the system getting damaged by high pressures, but also sets a level that allows the system to do its job and not vent water too much.

It is vital to ensure the relief valve is the correct specification for the desired use. The pressure rating of the tank must be greater than the pressure rating of the valve. In calorifier applications, the system can vent due to thermal expansion, which can be eradicated by fitting an expansion tank on the hot water side of the system.