FHW (hydronic) zone imbalance problem


I have an eichler with the heat in the floor. When the furnace was replaced, I had 2 zones plumbed, one for the main house, and one for a part of the house that didn't have heat installed.
I plumbed the second zone, using Slant/Fin, hooked it up, turned it on, and poof! the heat works just fine. Until the first zone comes on, then the second zone gets nothing. I'm not sure, but I think the first zone even pulls cold water backwards through the second one, because the second zone pipe turns cold quite quickly.
When the furnace was installed, both zones were run individually by separate pumps of the same size. No zone valves were used. But that pump wasn't strong enough to pump through the eichler floor, so the heating guys put in a bigger pump. The second zone has a smaller pump that works quite well when the first zone's not on.
I tried balancing the heat by adjusting the flow valves for the first zone. This works, the second zone gets heat, but I can tell the furnace is not working very hard, and the house doesn't come up to temp anymore.
I thought about hooking the zones up so only one can run at a time, but this won't work because the second zone is so small that it only drops the water temp by 10 or so degrees, and the furnace doesn't run until the water temp drops by 15 degrees, so the house is cold, and the furnace is not running.
Any ideas? I'm having the heating contractor come back and look at it next week but would appreciate any feedback.
Thanks
Rock
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IIWM I would have one pump and two zone valves. No reason to have two pumps unless the big pump for zone 1 pushes too fast or hard for zone 2.
Don't go for flo-control or check valves because they have to be set up very carefully to work properly.
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Why? Hundreds of thousands (or more) of homes have individual pumps for each zone. Mine works just fine that way.
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Two ideas
Get rid of the furnace and get a boiler. Furnaces heat air, but boilers heat water. Oh, you really do have a boiler.
Next, check for check valves in the system. You should have a device to prevent backflow so the zone pumps can work properly. Sounds like something may be missing or in incorrectly.
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The information on this newsgroup was worthless. Thanks a lot, guys.
Rock

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You got what you paid for.
<plonk>
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Regards,
Doug Miller (alphageek at milmac dot com)
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