Dear customer, I apology for my delay and i understand your question, in your case, of course, that the heater will not work while there is a coolant leak, basically because this system works in conjunction with the engine cooling system, for this reason, sometimes the heater to work properly you must wait a bit until the engine starts.
As you are in the presence of a leak in the cooling system, the heater motor will not be able to work properly.
This leak is a dangerous thing, because if the engine overheats or raises its temperature after a certain point it causes significant damage to it, which causes significant repair costs, you must correct this immediately and not use your Vans until corrected.
The first thing you should do is identify the exact location of the leak, it can be from the radiator, from the container or the coolant cap, or it can simply be a leaking hose, what you should do is go to a garage with a pressure gauge placed in the refrigeration system, this injects air into the system and increases the pressure in the pressure gauge, this pressure cannot decrease or yield, if it does you will locate the leak quickly.
Do you understand me dear customer?