Air running through the intake hose

I own an XP 3 that is 3 years old. I have not replaced any parts. I have a Rena smart heater attached to the intake. I am using the spray bar on the outake.

I have a RES, and lettuce frequently clogs the heater, but that does not seem to have caused any problems. The spray bar gets clogged because of hard water, so I have to rinse that out occasionally too. My filter set up is fine, and I clean them as required.

Recently there are large air bubbles coming through the intake, and then they seem to pass through the outtake. It is running loudly (water from the spray bar seems to be pressured by air pockets) and varies if air is coming through the spray bar.

I have checked all the hose connections, and everything seems to be fine and tight still. The air bubbles (large) come from the top of the intake tube all the way down to the filter, and then back up the outtake.
Several times a week the pump stops altogether and I have to reprime (the cap is put back on tight).

I have checked the turtle forums, who all use this filter, and have not found an answer. Could you please suggest a solution?

Regards,
Barbara Slatcher

 A: I can only give you general advice but the symptoms you describe sound like air is getting into the system someplace on the intake side. By process of elimination I suspect something wrong with the intake tube or connections, otherwise the air would not be in the intake when operating. The fact that you must reprime the intake tube tells me that the intake system is not holding prime and this reduces the siphoning action of the pump. It is possible that despite the tight filler cap on the intake tube air is still getting in around that seal. Air in the system causes the rotor to run dry due to a lack of water up in the rotor/impeller chamber. See the Performance Page in the FAQ section for many Q&A's on this subject.