[Rjcsjc62]

"No matter what the thermostat is set at (even 0 ), heat is still coming out of the pipes when the thing is set to automatic."

When you turn the thermostat to 0c is there still flow through the pipe? Or does it just stay hot for a while until the heat from the pipe/fins radiate?

Just so I understand, is this an existing system that used to work just fine, and now has problems. Or did you move there this summer and this is the first time your heater has been put to the test?

If there is no signal to the control valve from the thermostat, the control valve will stay open. When a control valve is not hooked up to anything or is just sitting on a shelf, or has no power to it at all, the valve will be open. It needs to be energized in order to close.

That is how your basic thermostat works. As your room heats up to the desired set point, the little mercury ball inside will slide over and make a connection between 2 contacts. This closes the circuit and energizes the control valve and tells it to close. The call for heat is satisfied and there is no flow in your heater. as the room cools down, the little mercury ball slides back leaving the 2 contacts open, therefore killing the signal to the control valve and opening the valve, allowing hot water flow through the heater, until your thermostat is satisfied.

This cycle just continues on and on all winter.

based on your story, my best guess would be that the controller on the control valve (often its a dome shaped, or mushroom shaped thing on top of the control valve) is broken and needs to be replaced. It is a common repair at this time of year. If you called a service plumber right now they will probably tell you it is one of several that they are replaceing that day.

In the meantime all you have is manual control. Ball valve open (handle parellel) = heat. Ball valve closed (handle perpindicular) no flow/no heat.

Unless I am missing something from not being there that is my best guess.