Are you the owner of an HHE-500-09M or another Aqua Hot/ Hydro Hot system and you can’t seem to get consistent hot water. Does your water seem to start hot then becomes cold? Could be your stir pump. This video can help you with most Aqua Hot system stir pump replacements. The stir pump circulates the boiler fluid from the bottom of the tank to the top so that the control thermostat has a more accurate temperature sense. Without this the burner wouldn’t kick on as fast as it should leaving you with a cold spike. Check it out.