Replacement Safety Pressure Valve for 12V Water Boiler from Expedition Upfitter. There is a safety valve (pressure relief valve) supplied with the water heater but if yours broke or you need a replacement this is it. Its function is to help decrease the pressure in the tank. The back pressure valve ensures that hot water does not flow back into the cold water supply. The safety valve has been preset rated to 7Bar in the factory. Do not adjust. This will drip water that's its function.