When the hot water circulator pump needs to be replaced, follow these steps.
Arrange your tools on a workbench or table so that they are clearly visible. Remove the circulator pump. Place a bucket underneath the marked area to catch any water that spills out when the bolts are removed. Loosen the flange bolts and remove them, leaving one in place to steady the existing pump and hold it in place. Measure the height of the new pump while the flanges are still attached to the pump. Use a saw to cut the pipe in the designated area and remove the existing circulator pump. Place the circulator pump between the existing flanges. Check to make sure that the water flow will be facing the right direction. Attach the gaskets or O-rings, whichever came with your hot water circulator pump, to the existing flanges to prevent future water leaks. Reconnect the electric to the pump.