What is done when changing a leaking heater control valve?

When changing a leaking heater control valve, draining the coolant is the necessary first step. This action is crucial because the heater control valve is part of the engine's cooling system, and coolant circulates through it. If the coolant isn't drained, it will spill out when the valve is removed, causing a mess as well as a potential safety hazard due to hot coolant.

Draining the coolant not only prevents leaks during the valve replacement but also allows for a cleaner and more manageable work environment. It is also essential to avoid contamination of the new valve and surrounding components by old, used coolant. After draining, the old valve can safely be removed and replaced with the new one, allowing for a proper assembly and re-filling of the system with coolant afterwards.

Other options, such as closing the valve or bringing the system to operating temperature, do not address the need to stop coolant from leaking during the replacement process. Putting the system in a vacuum is typically used for certain automotive processes, like evacuating air from the system or filling with coolant without introducing air, but it does not prevent leakage during the valve change.