A few customers have complained about a hissing sound coming from the pressurestat. If you look closely at the pictures below you can see a discoloration (greenish). It is limescale that created the opening in the elbow, then the descaler removed the limescale to cause a leak at the elbow. Descaler turns most boiler parts into a pinkish color. In this case, with machine unplugged and cold, one would need to remove the thermostat and then the elbow. Place thread seal tape around the threads of the elbow and tighten back on.