Can a blocked valley cause an internal leak?
Restricted flow can contribute to water backing up, but the valley material and adjoining roof details should also be checked.
Are gutter repairs roof plumbing?
Some drainage work may require an appropriately registered or licensed practitioner depending on the exact scope.
Will cleaning alone fix a leaking valley?
Cleaning may restore a restricted flow path, but damaged flashing, tile edges, joints, fall or water entering from above may still require repair.
Why does overflow happen only in heavy rain?
Rainfall intensity can expose capacity, outlet, fall or blockage issues that are not obvious in light rain. The wider drainage path needs context.
What details help with a gutter or valley enquiry?
Safe photos, the location of overflow or staining, roof type, storeys, recent weather and any known outlet or access constraints are useful.