Possible causes
- Damaged or badly fitted flashing kit
- Tiles not sitting correctly against the flashing
- Debris blocking the water channel above the window
- Condensation rather than a leak
Warning signs
- Water marks on the window lining
- Drips from the top of the frame during rain
- Damp plaster around the opening
Typical solutions
- Clearing and refitting the flashing
- Adjusting or replacing surrounding tiles
- Replacing the flashing kit
When to call a roofer
If water appears during rain rather than on cold mornings. Condensation and leaks look similar, so it's worth having checked.
This is general guidance. The cause of any roof problem can only be confirmed by inspecting the roof.