A very comprehensive Munchkin document set can be found here...
http://www.munchkinboiler.net/
A cursory look does not mention pressure - the "150" you mention has no units associated with it - any pressurised system should have a pressure release arangement to prevent explosion.
The documentation says... "Every Munchkin heater is equipped with a display which will read the outlet temperature of the heater and then will illuminate a green light showing flame on."
If it's leaking then you probably need to call in a specialist heating engineer.
Good luck...
Peccavi
October 2009