W220 Lamp Washer Operation

[bashers]

I've done plenty of work on my S320 now with help from here, other forums and mercedessource on youtube.
My S320 will not get through the next MOT this month if i cant get my lamp washer working and i'm struggling to get info.

When i press the button i get a pump running for a second, then stops.

I cant find many details about its workings online could anyone give me any pointers.
I can strip it and diagnose, but before i get it in bits, order/replace/repair what i need, refit it, await delivery, strip it again etc I'd like to know what i'm up against so i can make a speedy repair.
Its damn cold out there this time of year after all

How do i access the mechanism? Is it accessible from below. do i need to get the bumper off.
I can see the have not been jettisoned which seems to be common, but they don't pull out. should they?

I know this is controlled by an electronic fuse so is it possible it runs for one second then cuts out and resets.
Not ever seeing it run properly since i owned this car, should it run all the time i press the button or does it do a "cycle" when i press the button

 

[Minz]

Mine's a 204 but it works like this-

The headlamps are cleaned automatically if the "Wipe with washer fluid" function is operated five times while the lights are on and the engine is running. When you switch off the ignition, the automatic headlamp cleaning system is reset and counting is resumed from 0.