Am hooking up a new Weil boiler cg 5 There are 3 existing circulators ,all with there own power supply coming from 3 boxes in series. There is 1 thermostat wire, how can I tie them together?

You will need to use a master relay of sorts unless Weil has a built in relay system on the controls. If you do not know what you are doing STOP now and get ON SITE help.

NOTE: the CG-5 unit requires a major amount of outside combustion air to operate safetly.