If you see daylight behind all or some sections of guttering then this could be caused by the following.
Gap between roof tiles and guttering.
Broken tiles directly above the guttering.
Should there be a gap between roof tiles and guttering we have had birds nesting in roof and now possiblity that a rat has been in loft.
Sometimes the water shows up at a ceiling spot distant from the leak.
In fact in most places i was unable to get my fingers never mind my hand into the guttering to clear it.
Tiles not laid correctly above the guttering.
Guttering installed too low.
Logic tells me that this isn t right as heavy water flow off the tiles will surely just fly off the end of the tile and miss the guttering.
A gap behind the guttering that is allowing daylight between the gutter and the fascia.
Slowly move down the joint to apply a steady bead of caulk into.
Gutters should be hung where a straight edge laying on your roof shingles can easily extend over the front lip of the gutter this is the proper installment location for the high point of the gutter.
There is now a 1 2 inch air gap between the roof and the roofing tiles where the gutter guards were.
Looking right down the line of the guttering the gap between the end of the last roof tile and the outer edge of the guttering varies from around an inch and half to in some cases millimetres.
The gap can vary some because the gutters must slope towards the downspout.
A gap in the guttering itself.
Any more and you run the risk of water running off the tile and overshooting the gutter.
3 5 centimeters is in the 2 3 inch range.
In almost every instance gutter installers take the path of least resistance and shove the gutter right underneath the roof shingles instead.
If your ceiling has a plastic vapor barrier between the drywall and the attic insulation push the insulation aside and look for flow stains on the plastic often water runs to openings in the vapor barrier such as at ceiling light fixtures.