As per title, a little strange.

 

The rear washer jet comes on when using the front washer jets, rear works as should when using on its own 

 

Any thoughts

Are the front jets good and clear? Wondering if there is pressure building up.

Had a funny thing like that happen once.... Might have been a blown fuse but to be honest, I forgot about it till now. Try looking at all relevant fuses though. Proper checks, swap/replace if necessary. Also, check bonnet is shut properly although I think that was a different outcome.

46 minutes ago, Wonky said:

Are the front jets good and clear? Wondering if there is pressure building up.

Yeah both work strong and well when using but just rear squirts with the fronts

 

Will check fuse(s)