1 out of 3 heating zones not working

Our heating system seems to be operational... specially given the fact that 2 out of the three zones work like a charm.

The zone that doesn't work uses a "Honeywell V8043 E 1012 motorized valve", and since the problem started, we've replaced the motor only... and it didn't work. Now, we've replaced the entire valve, and we still have the same issue. In addition, if we set the valve to ON (instead of AUTO), the heating will work, but it'll warm up too much as there's no governor to tell it to stop heating.

We've also switched thermostats from the zones that work to the non-working one, and no deal.

Can someone please give us some ideas of what to look into to better troubleshoot and determine the root cause for our problem? ... as I'm writing this, it's making me belive that the wiring from the 2nd floor (problem zone) to the basement may be at fault... hope that's not the case. Anyways, any insight will be greatly appreciated.

Thanks,
Gus W.

sounds to me like a wiring problem........here's how it should be...from the
"R" terminal of your 24 volt transformer,up to the "RH" terminal on your thermostat,from "W" on the t-stat to one of the yellow wires in the zone valve,the other yellow goes to the "C" on the transformer........this is the same for all t-stats and thier corrosponding zone valves....now take 1 red wire from each zone valve,together they go to one "TT" or thermostat connection of the boiler....and the same with the other reds to the other "TT" or thermostat connection on the boiler.......thats all there is to zone valve wiring........if it still isnt working then there is a broken wire somewhere and you will have to check continuity on your t-stat wires...let us know how you make out.......

Thanks for all the input. We'll check and report back.

Thanks

Thank you again. After all, it was the wire from the valve to the thermostat in the 2nd floor that was the problem. The information you provided was very helpful, nonetheless, in narrowing down the problem.