Thermostat/Boiler Help

We have a boiler heating system in our house with 3 thermostats or heating zones. Two of them are working fine but the third, in the back part of the house, won't shut off. It will kick on when we adjust the thermostat but will not stop once the temperature is reached. It just keeps going and obviously makes that part of our house very hot. There are three White-Rodgers Zone-A-Flow Water Valves in the boiler room, I am guessing those have something to do with the stopping and starting of hot water flow. Last winter I manually turned the dials on all three of them to get the one out of control heating zones to stop. I think I've identified which water valve corresponds to heating zone in question. Does it seem logical that my problem could be resolved by simply buying and replacing that WR zone-a-flow water valve? And is that something I can do myself or will I need to hire an electrician? I hope that's enough info... Any help?
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On 9/15/2014 7:44 PM, BP1165 wrote:

First, determine which thermostat control which valve.
Noe you have to determine it the thermostat is turning off the valve. Two ways you can do this. If you have a meter, you can determine if the TS is keeping power to the valve. I had a situation where a weak TS battery did not have enough power to send the signal to make/break the circuit.
Another method is to connect one of the other TS to the offending vale Use a hair dryer to heat it to shut the heat down. If the valve stays open, it is probably defective.
The valves are fairly simple to replace and easy to wire.
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