[B]I have a forced hot water heating system with two zones. Whenever the first zone demands heat I hear a high pitched whistle. It seems to be louder at the first baseboard in the loop. Do not hear it at any other baseboards. Tried bleeding system but not too much pressure coming out of spigot. Any help would be appreciated.

Check system pressure if gauge is present. If zone valve has manual operator, move to open position & see if this has any impact.

What should the pressure be?

Typically 12-15 PSI for 1 or 2 story structure, 18 for 3 story.

I just checked and I brought it up to 15 psi and it still whistles. What is the proper way to purge system. I feel like there is not much pressure coming out of spigot. I recently install radiant floor heat under kitchen in the same loop. It started whistles not right away but after my furnace got cleaned two weeks later. The radiant heat added 200 feet of line to first loop.

If zone valve has manual operator, move to open position & see if this has any impact.

Did you check/try this yet?

You say you put the floor heat on the same loop? Did you put a mixing valve on the floor heat, may be something wrong with it. And do as kc asked open the zone valve manualy

I don't know how to manually open zone. What does it look like? There is a big green thing in line. If that is it how do I manually open it. And there is no mixing valve in radiant floor heat.

http://www.drillspot.com/pimages/54/5405_300.jpg

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I looked at the valve in line and it says universal flo chek. I unscrewed it and it still whistles. I can't find any valves like you have shown.

You may not have valves, you may have pumps running the zones. Do you have 3 pumps in this system?

Two circulator pumps

Is the pump itself making a noise?

I only seem to hear it in the room. I do not hear it near pump.