***Please Help*** I have a Pentair Minimax 400 inground pool heater that is 9 yrs old. When I turn it on, after @30sec it begins making a popping sound. At first I thought a rat or squirrel was in the heater and was jumping around. Took top off and did not find anything but isolated the sound to the flow valve assembly. Took this out and copper tip noted to be broken off. Just replaced with brand new one but still making popping noise in this area. Heater will only stay on for few seconds then shuts off. Technician at Pentair says pipes may be clogged but this is not the case. Any help would be greatly appreciated!