The weather forecast was completely wrong, the predicted rain never arrived and it was bright and sunny. A miracle. So I was up on the roof again.
Whenever it rains then one of the gutters overflows and a constant stream of water splashes noisily outside the window. It didn't need great detective powers to predict a blockage, so I borrowed a ladder and went up to see. Yes, there was a small pile of debris in the gutter and muck had piled up behind it.
While I had the ladder I looked round the rest of the guttering. Everything else clear. The one blockage was very close to the point where I had paid a roofer to fix the tiles. The suspicious part of me was alerted. Now surely he had an incentive to secretly create that little pile of mud, no immediate incident, but he would have known that after a few months this would eventually cause an overflow and, for those without tall ladders, another callout.