Dpg & Broadhoper,
I believe you nailed it 'Zone Valve' !
Called oil dealer service and described the problem, and they said 'Zone Valve' !
It appears to be only 1 zone in question.
I have Taco Zone valve, and supposedly they can be replaced easily, screw off, screw on ! Service tech on his way.
Thanks to you both ! Will report back after Tech reviews.
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