I have an all manual system and when the solar valve is on we continue to get air bubbles in the return lines. I replaced the vacuum release valve on the system. If I turn off the solar the bubbles will go away. It seems like an air leak as the pump has had trouble priming with the system on a few times. Is there a good way to check for an air leak on the solar panels? I don't see any water at all on the roof. Any advice would be appreciated.