Why are my gutters overflowing even though they look clean?

Gutters that overflow despite looking clean usually have a clogged or undersized downspout, incorrect pitch so water pools instead of draining, or runs that are too small for the roof's water volume. A flow test finds the real cause, which is often the downspout, not the gutter trough.

Overflow isn't always about leaves in the trough. The most common hidden cause is a downspout clogged at the elbow or underground, so water backs up and spills over. Other culprits are improper pitch — if a run is level or tilts the wrong way, water sits and overflows in heavy rain — and undersized gutters or too few downspouts for a large or steep roof. We run a water flow test on the whole system to pinpoint where it's failing, then correct the pitch, clear or resize the downspout, or add capacity. That's a far cheaper fix than assuming you need all-new gutters.