If the breaker is not tripping I can't see why it would be suspect. Years of troubleshooting have taught me to look for the last thing that has changed - in this case it was the pressure sensor. I'll bet a cold beverge of your choice that the problem is related to either the device, the install of the device, or a further problem not yet diagnosed.
What is different between a power is cycled at the unit and power cycled at the breaker? Something may be in front of the local disconnect. I have seen control transformer leads on the line side of too many disconnects.
If it were me - I would...
1. Revisit the pressure sensor change - why did it fail and was the replacement of the same range and output.
2. Determine the difference between cycling the power locally and via the breaker...this is telling you something.
You can measure the voltage at start-up and you can measure the voltage drop across the breaker however I think you are chasing you tail as the unit operated with that breaker before.
Let us know how you make out. Mike
