replumbing hot water boiler

[handydan]

Hi
I am getting ready to replace a bunch of very messed up plumbing in the basement of my very old house. One thing I would like to do is replace the 1/2" copper supply & feed lines to my Hot water Boiler with 3/4 pex. The connections are made to vertical 3/4" copper pipes on the back of the boiler & I am wondering what kind of trouble I could get into. How do I make sure there is no pressure in the pipes? Does the boiler need to be shut down? (The boiler, unlike the rest of my house is a new state of the art Viessman). 

[PlumbingHelp]

If your talking about the make-up water to the boiler than 1/2" is plenty. If you have a new pressure regulating valve on the make-up line it has a built in check valve that should keep the boilers water in the system while you change the line. If water leaks by, you will have to be prepared to isolate the boiler.
If you want, you can upload photos to the gallery. Helps me understand what your doing.

[handydan]

I guess I left out some important details. The boiler sits on top of a domestic hot water storage tank. While the boiler does get its make up water from this supply line it primarily feeds the hot water tank. The boiler is 25' away from the rest of the house plumbing & I am hoping that by increasing the lines to 3/4" I will see an increase in water flow.

[PlumbingHelp]

Well, it's a little hard to see whats going on there, but if you run the replacement water supply then shut down and isolate the boiler (valves) you should be done in no time.
Is that black iron pipe and copper mixed together on your potable system?

[handydan]

Thanks, I think I will be ok. The black iron pipe that you see is boiler water going through the hot water storage tank, it doesn't mix with the potable water.
I haven't started yet so I'm sure I will be back with more questions soon.