home heating system?

I have a myson apollo boiler it is either the 15/30b or 30/50b model.I have been having some problems with lately in january it went off altogether could not even get pilot to light,this was resolved by replacing the thermocouple. Then amonth later it went off again this was resolved by relacing the limit stat.Now aweek later it has failed again, ican get pilot to reignite burners fire up radiators and water begin to warm but after about 10 to 15 minutes it cuts out completely.The guy who installed the parts for me is out of town tillnext week i was just wondering if anyone could help with what the problem may be and what part may need replacing so i can order it.

petermac
March 2010