How's this?
A few days we had our Annual Central Heating service. Usually they can check everything from inside the house and garage, but this time they needed to go under the floor.
While the hatch was open my husband noticed soe wetness on the ground. After the engineers had gone he went down to investigate and saw that the water was running down from above the floor and that the floorboards were wet.
We then spent the next couple of evenings crawling about under the floor investigating and came to the conclusion that it was the waste pipe from the bathroom upstairs that was leaking, (It's all fixed now)
How lucky were we that the engineers had to go under the floor and hubby happened to look in the hatch and spot the wetness? If the hatch hadn't been opened would we not have known about the leak until, at best, something electrical stopped working, or ,at worst, the house blew up? Because the water was running over some wiring.