Debris can collect where tile roof slopes meet and interfere with drainage. The amount visible from the ground may not reflect what is trapped beneath nearby tile edges. Clearing a valley also requires protecting fragile roof materials during access.
What to do next
Arrange a professional assessment rather than walking across the tiles yourself. Ask whether the work includes checking the valley detail for deterioration or damage. Keep cleaning and repair findings separate so you know whether the issue was obstruction, a failed component, or both.
Related Perkins guidance
Contact Perkins Roofing to discuss your roof and the appropriate next step.