[danno]

What is causing these lines? 4th time iv cleaned this place been fine everytime till now all of a sudden this is happening... can anyone help

[Soupy]

My guess is it's either the vent or the paint on the wall. Run your finger on the paint and see if it comes off on your finger.

[supernova77]

It's either water dripping out of the vent... Or water is getting behind the vent and then running down the glass after the you've cleaned...

Andy

[SeanK]

Would agree, vents can be problematic some don't give any problems others leak
for hours.
Best avoided in my opinion.

[danno]

Its coming over the top of the frames sure its something to do with the walls. Its a recently converted house.

[SB Cleaning]

I'd say it's the painted wall are you cleaning above the vent?

[danno]

Is the picture working?

[SB Cleaning]

Is the picture working?

As a few of us have replied with an answer to your problem I'd say so

[Bungle]

What is causing these lines? 4th time iv cleaned this place been fine everytime till now all of a sudden this is happening... can anyone help

Looks like you are cleaning the top frame as you can see the lines on the side frame too. Try buffering your brush up to the top frame, but not above where the glass meets the frame. Coming from either the vent or cheap emulsion I'd say.

BTW love the pic of Vale 

[Soupy]

[Elfyn]

I think the paint on the walls is lime wash - big problems if it is 

[SherwoodCleaningSe]

Looks like you have staining on the frames as well.  I'd say it's nothing to do with the vents and something to do with the walls or paint.  Does it come off with a wet and dry cloth?  It might end up staining the glass.

Simon.

[Elfyn]

I've seen lime wash "paint" etch glass and permanently mark frames.

[Dave Willis]

It's the paint on the render. They haven't built a lip on the wall to divert the run off from the windows. You'll get that after every drop of rain.

[Chris Buchan]

Not the vents,you can clearly see it coming from the wall over the top frame and down the glass.

Just stay away from top frame and do glass.

[Mike #1]

Their is a good chance that after you have cleaned the upstairs windows that the water is running down the rendering and this is the runs plus the water you have used on downstairs windows is adding to this .

Clean all upstairs windows first then do downstairs hopefully allowing time for water from upper windows to run down and dry out . I have a similar issue with one house and it is caused as explained above . Mike

[danno]

It came off ok when i went back over it today i just wiped the frame and rinsed the glass. Come to think of it the day i did them last it was lightly raining, must be either lime wash or paint running 

[danno]

Appreciate all the replys. Very helpfull 

[Paul Coleman]

If the water is coming from a frame above and the render, do a final brush on the upper sill without water running.  This will reduce the time needed till upper frame stops dripping.  As soon as it rains the marks will probably be back anyway.  This is also a problem when walls are painted as the brickwork doesn't absord the water easily.  Similar thing with shiplap on walls too.

[Richard ham]

As its on the frame also its not the vent. Its from the dodgy render and paint, probably cheap paint too. If its just that window I would try it the old fashioned way, get your squeegee out. If its all of the windows I would graciously decline to clean them.