Sadly we don't get headlamp washers in the US. I did retrofit some on a previous Subaru using OEM parts. I don't know if it's set up similar to the front and rear washers on cars with rear washers. But if you look at the washer fluid tank, the pump for the rear washer is located higher up on the tank. This is so if you are low on fluid, it gives priority to the windscreen washing. Maybe it's a similar situation? Is the tank full of fluid? If it is it might be a clogged line. Most of the sprayer systems have check valves close to the spray nozzles. This keeps fluid close to the sprayer so it sprays faster. I've seen those get clogged from time to time.