Your question is the circulator is running 100% of the time regardless of the thermostat setting? Is this a new problem or had the same problem before and it has shown its ugly head again? What are you using for heat? A tankless system or a condensing boiler?
What are you using for a controller? Something is turing on the circulator? A faulty thermostat could do it but they rarely fail. The controller should have a relay that turns on the circulator pump and its contacts may have burned together thus not braking the contacts open.
If you can, disconnect the 24v's to the controller. If the pump turns off reconnect the 24v's and disconnect the thermostat wiring. If the pump runs suspect the controller is the issue. If it doesn't not run suspect the thermostat or its wiring.
The past problems are the same as now or just different problems?
