Does each zone have its own pump or are they controlled by valves with a single pump? Is the circulator pump starting up when heat is called for on the second floor?

Hi thank you for replying. There is only one pump. Three zones have an individual controller but has no shutoff valve. The pump does responds to when I turn the temperature setting of the second floor up. But hot water does not circulate and the pump kept on forever, so I am keeping the setting low.

See if you detect opening and closing of the individual control valves as they respond to the thermostats. It might be easier to detect opening and closing if you have another loop operating since that eliminates the pump starting at the same time. This might be most easily done with a helper operating the thermostats or disconnecting the thermostats at the boiler and closing the control circuit there.

I am taking back my statement that the controller for the second floor is working... I have turned up the thermostat on the second floor all the way and the pump did not kick start. Could this mean that the controller had gone bad? I plan to do a few more control experiment tonight. I still cannot eliminate the possibility of frozen pipe, because if you manually turn on the valve to the second floor while the pump is on, water still does not circulate to the second floor.