14-3??? Holy cow!!! That's huge wire for a low voltage thermostat. I'm somewhat surprised that you managed to get that wire around the screws on the zone valve and the thermostat. Since this is wiring less than 50 volts, then you can splice it however you like. Normally, thermostats and zone valves are connected with 18 gauge "thermostat wire".
"Nothing is foolproof to a sufficiently talented fool"