Pentair Max E Therm MasterTemp Air Flow Switch (42001 0061S) thermproducts The after 2003 model compatibility and The after 2003 model compatibility and quantity of eight format give this set practical value because sand filter internals work best when they match the original model generation and quantity relationship closely while the connection format helps preserve compatibility in systems built around this specific plumbing configuration confirming that the combustion air system is operating before the heater continues through startup or diagnostic issues when the blower and venting system are otherwise serviceable