Your expansion tank, for whatever reason, is too small to do the job properly. http://64.226.150.132/hydronic/des/start.htm#Expansion
There is little maintenance to be done to a hot water system. The important task is to make sure the pressure does not drop below the minimum, which indicates a leak. Leaks should be repaired immediately. Keeping the hand valve to the pressure reducing valve makes sure that you pay attention instead of permittiing the valve to feed water through a leak.
Calling a repairman yearly to check the combustion components yearly is also important.
You can use the instructions from other manufacturers to follow manufacturer’s instructions. Weil McLain and Burnham have excellent installation and owner manuals available on the web.
