What can I do to stop the knocking in the pipes as the pressure builds up

Need more information on your system. Steam (single pipe or)? Hot water? Number of stories? BTU capability? How long has this been going on? It is difficult if not impossible to get the feel of the circumstances with no info.

Single pipe system not sure about BTU but when the water heats up in the boiler steam is sent through the pipes hope this can help you to help me

Sorry about y reply delay. First check to see what your water level is in the sight glass. Boilers usually bang around when too much water is in the boiler. Anything over 1/2 full can be a problem. Naturally while you are at it I would also drain some of the boiler water off from the drain cock at the bottom and see how dirty it is. If this boiler has not been serviced this year now is the time to get a pro to look it over since I never recommend that type of work to be done unless you are experienced with steam generators/boilers. Hot water is one thing but steam is a different animal.