The following video explains a very common issue reported with solar pool heating systems. Solar pool heaters rely on adequate flow for proper operation. If the flow rate gets too low, air is let into the system through the vacuum relief valve, which allows air into the panels when a vacuum exists to protect the panels and plumbing from collapsing. The resolution is usually as simple as cleaning or replacing your filter cartridge. A dirty filter increases pressure on the pump, decreasing flow, and stops the vacuum relief valve from closing completely. Air gets into the system, reducing performance and causing bubbles in the pool.