Why is the room hot when I don't set the t-stat to call for heat

John@Reliable_14

just take off the wire from top #1 screw on the zone head that overheating, if it stops heating you have wiring trouble. If it still heats you have a bad/stuck zone valve. Cheaper to call someone in the long run, savings just in the cost of gas returning all the parts you brought is about the cost of a service call

Finalcut

Why is the room hot when the T-stat is not calling for heat?

I have a Burnham boiler with one circulation pump and three t-stat/Taco valve controlled heating zones. Two zones work fine. The third zone, which has worked fine until recently, has hot water flowing through it when the t-stat is set lower then the room temperature.
I've swapped out the Taco valve power head for the zone that isn't working and had no change. I'm getting 24 volts at the Taco valve when the t-stat is off, when it is set 11 degrees higher than room T, and when it is set below room T. ??? On the other two Taco valves I get 24 volts when T is set 11 degrees higher than room T (call for heat) and zero volts when t-stat is turned off or set lower than room T. I've swapped out the t-stat (three different ones) on the bad zone and still no change. Before I trace all of the wiring, which I'm dreading, any advice?