If that was the only valve, it was closed, and the thermostat called for heat, it doesn't help the circulator if it runs against a closed valve. May not hurt it, but it doesn't help. If the pump ran dry because there was air in the system, since the bearings are lubricated by the water, that would cause it to wear out. If the pump is oversized, I guess it's possible you could get some cavitation, which would make noise.





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