How to Check Your Downpipes Are Running Clear (Safely, From the Ground)
A gutter that looks clear can still overflow if the downpipe underneath it is blocked. This is one of the easiest things to check without going anywhere near a ladder.
The simple test
During or just after rain, watch the base of each downpipe where it meets the gulley or drain. A steady trickle or flow means it is working. No water at all, or water leaking from a joint partway down the pipe, points to a blockage above that point.
What usually blocks a downpipe
Leaves collecting at the swan-neck bend near the top is the most common cause, followed by moss washed down from the roof further down the run.
Stop and call a professional if: the downpipe is still not draining after an obvious surface blockage has been cleared, which can mean a collapsed or disconnected section underground that needs proper drainage work, not a gutter clean.