Why is my forced-hot-water system heating when the circulator pump is not running?

I have a forced-hot-water heating system with three zones, first floor, second floor, and water tank. After some maintenance on the system the second floor is constantly heating, even though the thermostat is off. I checked the voltage on the circulator pump and it is zero, so the pump is not running. It sounds like it is acting like a gravity-fed system. There are manual valves on the system, but the only things in the loops that are controlled by the thermostats are the circulator pumps. Do the pumps act as valves when they are not pumping? That was my guess so I replaced the pump, but my registers are still hot. If the pump does NOT act as a valve, what is supposed to prevent the hot water from moving through the system when the pumps are not running? I need some HVAC basics here. Thanks!

Why is my forced-hot-water system heating when the circulator pump is not running?
It sounds like your flow control valve is stuck! The circulator pumps does not act like a valve. you said you had maintenance done. the person doing the maintenance could have turned the lever on the flow control valve accidentally causing it to gravity feed. If the lever did not get turned TAP on it with a hammer sometimes rust will cause the valve to stick open. I would tap on it first if you are not sure if the valve got turned or not.
Reply:You should have a control valve that is hooked up to the thermostat that will throttle the water flow to meet the thermostat's temperature demand. When there is no demand (temperature is made), the control valve should shut off all the flow to that zone. Sounds like this may have malfunctioned on you.
Reply:probably jus an in line impeller - water will pass w/o juice due to heat rising %26amp; COLD dropping on the other side... just not as effecient!



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