[KS Cleaning]

What causes the black run marks that you get on some white UPVC frames? even some  newer windows seem to suffer from these unsightly marks,  I'm guessing it could be from cheap rubber seals?
Anyone know of a product which can get rid of these marks?

[Positivity]

I think it is airborne pollution as much as the rubber seals because I do some houses with white seals and they still have the "tiger stripes" on the front of the sills.

[SeanK]

Yes they come from the rubber seals usually below an opener with a faulty drain hole, once they get ingrained they
can be a nightmare to remove and should be considered an add on job at an extra cost.

[SeanK]

I think it is airborne pollution as much as the rubber seals because I do some houses with white seals and they still have the "tiger stripes" on the front of the sills.

You may find that the draught seal around the inside of the opener isn't white and sits below the drain hole, even if white
they never get cleaned so slowly leak dirty water onto the frame below.

[Smurf]

I've found the easiest way to clean filthy, discoloured/stained plastics back to white is to use soft wash method as shown in this vid. https://www.youtube.com/watch?v=DqvABSlIBv4

[NWH]

These  Windows are what gives WFP a terrible name,they look awful after being cleaned by WFP. I've gone and done insides and had to trad most of these type of Windows thankfully they don't fit many windows like this these days the seals are now recessed in the frame ,TBH honest if I get asked to do places with these windows I walk.

[nathankaye]

When i trad cleaned these, i did same method as i do now on wfp.
Wash the life out of the seal, esp side ons and bottom. They streak badly but eventually stops and i dont seem to have any problems for a good while. At least, thats what i found.