I have a oil fired boiler with taco 562 zone valves.My wires are from transformer red&green.Wire from thermostat are red& green.On my zone valves the wires are red,green&yellow.Aperson who said he could fix zone valves had taken all wires off the zone valves.The zone valves have numbers 1,2,3,which wires should go to what number.
I would be thankful for any help.

General wiring:
http://www.centralboiler.com/Tech/C160.pdf

This shows a 3 terminal Honeywell device where 1 terminal is "blind". Not connected, but used for convience.

http://customer.honeywell.com/Techli...95C-10938B.pdf

If that's the case, you may be able to mechanically inspect the terminals.

You can also use an ohmmeter. The 2 with a resistance is the valve. The left-over termimnal is "blind" and used for convience.

You may find this site more useful. The Taco zone valve

Likely the yellow wire comes from a double throw relay. When the thermostat calls for heat, power flows to both the boiler controls and the coil of the relay. The relay switches power from the wire to the # 3 terminal to #1, the valve opens, shutting the motor off when it is open. When the thermostat shuts off, the relay switches bower back to the #3 terminal which then closes the valve. There should be one wire, the red I guess, that goes from the transformer to the thermostat. The other wire from the transformer is the common, going to the boiler controls, the relay, and the #2 terminal on the zone valves. The green wire from the thermostat will go back to the boiler controls and to the relay. The relay should be marked NCC and NOC. Try connecting NOC to # 1, and NCC to #3. If it works backwards, reverse them.

labman:

Nice job. Here's taco's website: TACO - HVAC
So, one terminal is not likely blank based on your information.