back windscreen wiper wash

Guys, I dont know if its a problem with my new V70, but when I try and jet wash the back window the wiper does not come on automatically. I cant see a reason for this and its the first car that I have driven thats not done it. My 54 plate v70 was fine, three wipes and the window was clean. I have to manually press the button for the wiper now.

does it come on when you select reverse when the front wipers are going?

yes, if the front wipers are on and you put it in reverse then the back wipers will come on. Just not when I use the jet wash