I think this unit has a utility valve on the front. If so, do you have good suction at this valve? If not, disconnect the inlet piping and check the suction directly from the inlet. Make sure the utility valve is closed while checking the suction on the inlet. If you have good suction, you have an open pipe or valve somewhere in the house. If you have any vacpans, check these first. Next, turn the unit on and walk through the house and listen for air whistling. If you do not have good suction from the inlet at the unit with the utility valve closed, replace your bag and look for a secondary filter that may be plugged. Good Luck!