Thermostat works, Zone valve works, but boiler won't fire for one zone.

I have a 12 yr old Utica gas furnace with 3 zones. I recently changed out the hot water circulating pump, expansion tank, and bled out the system in the process.

Noticed today that Zone 1 wasn't calling for heat with the thermostat on; checked out the zone valve which was warm-hot (the motor portion, not the box/casing), and the valve was open, but wasn't making the boiler turn on.

1. So i changed out the thermostat to see if that was the culprit; nope.
   
2. I changed out the valve motor with the motor from for Zone 3 (basement) which works (i didn't have a working spare handy), to see if it was the motor gone bad, even though, as i noted, the valve does open; no difference.
   
3. I thought perhaps it's the end switch, so i changed out the entire zone valve assembly for Zone 3 in to Zone 1 (still wired to the Zone 3 thermostat) and raised the thermostat for Zone 3 to see if that would send heat to Zone 1. I mean... it should, right? But nope, same thing - the valve is open but it will not turn on the boiler.
   

I'm perplexed. If i used the zone valve assembly that works for Zone 3, it should work for Zone 1, if i use it for that, right? The only thing i can think if is that the zone valve for Zone 3 is also going bad (the end switch), but since it's for the basement (where the boiler is located) it's somehow still managing to turn the furnace on (because of the short wiring distance?), but it won't for Zone 1 when i use it to try to make it work for Zone 1.

Any ideas? Thanks!