Before testing this you can attempt to mix a citric acid solution in with your water in your water tank and draw about 4 ounces of the solution into your machine into the machine. If you run the group head for 14 seconds you'll have drawn about 4 ounces. Once this is done turn your machine off.
This will saturate the descale solution in the inlet assembly so that any scale on the check valve will be loosened and removed. After 45 minutes of waiting dump out the citric acid solution from your water tank and refill it with regular water. Draw 8 ounces of water out of the group head to get all of the citric acid out of the inlet assembly and then follow these instructions to drain the boilers and refill them with fresh water. If your machine is still leaking follow the instructions below.
First, remove the panels.
Rebuild and test