Thank you! I wouldn't worry much about the pipe bursting then.Doesn't matter if pump is before or after boiler because the pump is a circulator just moves water around rather than like a well pump that takes a few pounds of pressure and raises it 50 to 100's of lbs. There is no problem if the pressure is a few lbs high. Boiler relief valve with blow off at 30lbs.
Heres a chart for working and bursting pressure for black pipe.