The present invention provides a fluid injection system (11) which transitions between a maintenance mode wherein an outlet (15) is closed and no fluid is discharged through the outlet, and an operation mode, wherein the outlet is open and fluid is discharged through the outlet. The fluid injection system injects a first fluid transported in a first pipeline (21) with a second fluid, wherein there is a temperature differential between the first fluid and the second fluid. The fluid injection system comprises a holding tank (49) for storing the second fluid, a cooling means (35) to cool the second fluid, and a pump (39) for delivering the second fluid into the first pipeline. The second fluid mixes with the first fluid in the first pipeline to provide a combined third fluid having a temperature within a predetermined temperature range, wherein the third fluid is maintained within the predetermined temperature range when the fluid injection system is in either mode such that the temperature of the third fluid made available to an outlet is within the predetermined temperature range.