Heat always on in one zone? Troubleshooting dead-end...


Old 02-24-18, 02:36 PM
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Question Heat always on in one zone? Troubleshooting dead-end...

Hello - hoping someone here can help.

My home has an oil-fired boiler. There are five zones with circulator pumps on the return side of each zone.
We noticed last week that no matter what the thermostat was set at (even if off), the baseboard units were always pumping out heat. Ohm-ed out the thermostat cable, it's good. The thermostat also appear to be working fine (when turned above ambient the relay at the aquastat pulls in fine and we can feel/hear the circulator pump for that zone come on. Likewise, when the thermostat is off, the relay is open and the circulator pump is idle.
I still have heat in this zone however (all the time) even with the circulator off. I'm not sure what to do/look at next...? Help?

Thank you!
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Old 02-24-18, 04:02 PM
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Every zone that is controlled by a pump must have a Flocontrol valve, usually on the supply side of the zone coming off the boiler.

It takes the operation of the pump to that zone to for the flapper open and allow water to flow through the zone and back to the boiler.

That FCV has a screw or thumb screw on top, when turned counter clockwise opens the valve to a manual setting allowing water to flow no matter what zone calls or if the boiler has a tankless coil, will flow by gravity uo the pipe.

Check that valve to see if someone for to clos the screw maybe after bleeding the zone.

If the screw is wound all the way down then the flapper could be stuck open. Give it a wrap with a hammer to see if that helps to close it.

If you are sure the pump is off that is the only way for unwanted flow to enter that zone.

Pics of the boiler and piping would be helpful if more help is required.

Hope this helps a little.
Old 02-25-18, 09:42 AM
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Some circulators have flow control valves built in. If you don't have an external flow control valve for the zone giving you trouble, it's likely the internal FCV is stuck.

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