I have been told that copper 3" mains fitted between cast is a problem Does anyone know why??? The main is mostly cast80ft. someone-(previous owner) replaced 18 feet of cast 2yrs ago with 3" copper Also-there is approx.6ft of 2"galvinized pipe running vertical from the main down to the return. Both of these pipes are above the water line. What damage is these different metals doing to the rest of the cast,or worse yet,the boiler???