Installing new Thermostat without a common wire

Question

My old thermostat did not have a common wire...the new one has a connection for one. Do I have to run a new wire?

Answer 1

no use the wires you have hook them up on the new one y r g w by the way if your install new t-state because its not working its your system not the t-stat t-stat is control only

Answer 2

If your thermostat requires the 24V for operation you might have to have it.  Most thermostats I have seen don't require it.  Read the manual that came with your new thermostat.  It will tell you.