I had a Honeywell T8600D 2028 Chronotherm IV that worked fine until soda got spilled on it. I now have a Honeywell T8601D 2019 Chrontherm IV replacement that I want to install. System is a 1980’s single zone, oil fired, circulated hot water, baseboard heat only.Furnace is controlled by a Honeywell L8124C1003 Triple Aquastat. The old HW T8600D worked fine with the two thermostat wires from the aquastat connected to the “R” and “W” terminals. I can get the new T8601 to turn on and accept time and program inputs when I connect the two existing thermostat wires coming from the aquastat “T” terminals to the new thermostat “C” and “R” terminals. When the thermostat calls for heat, I get a small flame symbol on the display panel, but the aquastat is not starting the circulator. I am not understanding the extra "C" terminal on the new thermostat. Do I need another wire in here someplace? Any suggestions how to get the circulator running when the thermostat calls for heat?

Thank you in advance for any help and indulgence with my amateur problem. I have a residential heat-only radiant system. The system has a number of zones, each controlled by a valve. The valves are connected to a relay board. On the relay board, I just need a thermostat to close the link on two input wires to turn on a zone. Most of the house is controlled by Upinor radiant thermostats which are simple 2-wire units, and I just hook up the two wires and it works fine. One zone was not wired, and I am installing a honeywell wireless thermostat to control that room. I am having some difficulty wiring the receiver to the relay board. I wired 24VAC out from the relay panel, Common to C and the hot to R (and bridged to Rc and Rh). The power seems to work fine, the receiver connects to the thermostat transmitter, and if I turn up the setting the heat circuit flips on the receiver and the heat light goes on. So I need to hook two wires from the receiver to the relay panel to close the loop when the system should be heating. I thought from reading the manual that the outputs should be the W wire, and a splice off the common coming into the receiver unit. But this does not trip the relay when the heat goes on. Can anyone help me with how I should wire to the red and white inputs on the relay panel? Thank you for your help. Relay panel: [IMG]http://dl.dropbox.com/u/86495/photo%20%281%29.JPG[/IMG] Thermostat receiver: [IMG]http://dl.dropbox.com/u/86495/photo.JPG[/IMG]