The leak is easy to recognize from the traces of lime under the heater.

A leaking expansion chamber is usually the cause. But also check whether the connections on the heater are not leaking. The water may also come from above, e.g. from the upper brewing flask.

If too much water is running in/through the expansion chamber to the drip tray outlet or next to it, you can check where it's coming from by unplugging the silicone hoses. You may need to replace one of the following components:

from a defective pressure relief valve in front of the heater

from a leaking steam valve

from the upper brew piston if it is defective/leaky

If you start the machine - with all caution - you can observe where the water comes from. Immediately pull out the power plug.