Water coming over gutters

When it rains hard there seems to be too much water for my guttering to cope with and it comes over the top in one particular area.

We live in a mid terraced house and we have a downpipe, the guttering is only 1 year old and is plastic. I have noticed the area it overflows is where we have a Velux is this causing it? Is this something to worry about?

Thanks.

there may be leaves and crud blocking the outlet. check here first.

if the guttering has been fitted poorly ie, without a line, there may be dips.

large gaps between clips/brackets also causes dips.

finally, union brackets can also be a problem as these always seem to cause a low spot even when fitted to a line. when we fix gutter, the clips are fitted to the line and the union brackets are fitted after the gutter has been clipped in. we then eyeball it down and pop a screw into the union, when in line.