Water Under the Boiler: Three Possible Causes
The first is a leak inside the casing: a failed seal, a weeping pump or a component that has corroded through. That is a boiler repair, and it needs a Gas Safe registered engineer because it means opening the appliance.
The second is a leak in the pipework just below, at the valves or joints where the boiler connects to the system, which drips down and looks like the boiler. The third is the pressure relief valve: if system pressure climbs too high, it lets water out through a pipe to the outside wall, and a drip there points to a pressure problem rather than a hole. We check all three before deciding what needs doing.