Testing a new system loop prior to installing tile and radiator

Old 07-03-13, 12:08 PM
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Testing a new system loop prior to installing tile and radiator

I have a simple question. Im adding a radiator to my existing hot-water heating system in my 2nd floor bath. Ive done the piping and want to test for leaks before I close up the bath floor and lay tile. The piping is shown in the drawing below. The new tertiary supply and return are only 2 apart where they will join with the radiator. Currently they are joined with a 2 horizontal length of pipe so I can run water through them to check for leaks. A potential problem is that my plumber installed the temporary bleed valve on the supply side 5 below the turn. When I test the system, the supply side gets hot but the return remains cold at the basement level. I infer that water is not making the U turn back down to the basement. Could this be caused by air trapped at the U turn that cant be bled because of where the bleed valve is? If so, would it be ok to put the bleed valve on the return side below the U turn, or must it be at the high point?

Thanks in advance for your help.

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Old 07-03-13, 12:48 PM
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Air vents ALWAYS go at the top of the return side. You are correct that the "U" is an air trap and that is the primary reason why the water won't circulate. Air vents are somewhat passe these days and many systems use a power purge design to completely eliminate air but I prefer real air vents.
Old 07-03-13, 02:31 PM
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I prefer real air vents.
Me too...

"Power purging" is a vicious circle, a Catch 22, damned if you do and damned if you don't.

The point is to get the air OUT of the piping, and by doing a 'power purge' and pumping fresh water back in, you are adding all that dissolved air right back into the system.

When you install the new rads, add a manual coin slot bleeder valve on the DOWNSTREAM end of the rad... like this:

When the pump is running, air will collect at that point, so that's where the bleeder should be.

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