Baxi Boston 2 80RS Boiler. It all started when I called in the heating engineer to Power flush the system. 2 days after (back last April) I noticed the last radiator was not getting hot, not even warm. I called them back and they tried to balance the system (which was working perfectly before). They came around for a few days but they couldn't solve the problem, they told me that there must be trapped air somewhere and it would eventually work its way out of the system. It hasn't and they have given up. I was also charged for a new pump, but that didn't solve anything. I now need to make sure that the system is working correctly for this winter. I am getting rumblings from the Boiler, when the boiler is on for the water. Does that tell anyone what the problem may be?? Is there an air vent on the boiler maybe??