Watermarks above windowsill. Pics attached.

[skippy67]

We live in a 1930s semi. Over the last few months this stain has appeared one side of the bay window in the front room. I can't be sure, but I think similar is staying to happen on the other side too.The windows are UPVC double glazed about 15 years old. We're in London, so no extreme weather really. Do I need a glazier or a builder or both??

We've had this on two occasions, one was in our recent loft conversion so we had the builder come back and fix it (there was a gap somewhere that water was getting into, they sealed it and it's been fine since.)

The other time was on a downstairs window and we called the window company that had done the install a couple of years earlier and they came out and dealt with it. So my answer doesn't really help with who specifically you need but in our case both were able to sort it! I'd probably call a builder in different circumstances as the water could be getting in somewhere else and window company couldn't sort that.

I had similar in my front room when I first moved into my house. It turned out to be blocked gutters. Once the area dried out I was able to repaint it.