Faulty circulator: Check the circulator. You will find there's spring-loaded coupling that connects the pump on the motor; when it breaks after the pump jams, the coupling could make a loud sound as the motor operates. A bad circulator pump will require to be replaced by a technician. This move http://plumbersbarrowinfurness14691.ampblogs.com/Plumbers-Barrow-No-Further-a-Mystery-31702014