Rinnai i150sn condensing boiler. What is this button that the arrow is pointing to om the pressure sensor casing?

[dudemanbro]

As others have found my pressure sensor seems to be fluctuating with a mind of its own. Out of curiosity what is this button that the arrow is pointing to on the pressure sensor casing?

 

[LoganB Plumber]

I have had the same troubles with a Rinnai I 120 solo . Tech support sent out a new sensor which also included a new adapter fitting that accepts the sensor into the top instead of the side . They said it would be better . Worked for roughly 9 months and went back to the same problem . I put another sensor in it today .