UPVC Soffits need cleaning- what to use

Dilly

Hi
I have soffits on aa single storey extension. I have noticed that they have grey water runs / marks and also when scrubbed there is, in some places, a kind of build up of ???? Its a creamy colour and is rough!
I have washed the boards and used  HG UPVC Cleaner and 'The Pink Stuff' cleaner. This has not made any difference to the marks. 
I tried I also tried a limescale cleaner on the rough places and although it did not fizz after much scrubbing, some did come off. But there's a load more to do
Can anyone recommend a cleaner that will remove these stains and also if anyone knows what this hard build up of matter is I should be very glad to know
Thanks in advance

Grenage

Ciff/jiff is excellent on uPVC.

greenface2

go to gap or eurocell type of upvc supplier and get some solvent cleaner (smells like pear drops) should do it . cream cleaner maybe too mild . or try some wd40 first with a green sponge pan scrubber see how that goes . there is also a cleaner called rhino goo and zep90 . haven't seen it for some time . its strong stuff . only do this if its white soffit 

Spinybif

Everbuild UPVC cleaner, available from Toolstation, Amazon etc.