I just learned something today after struggling and searching for a few days. I thought this info may help someone.
I replaced my Pentair Mastertemp 250HD with a slightly used ($1500) Pentair Mastertemp 400HD model 461021 ASTM, an exact fit so it would be an easy install. However. I could not get the pool water inlet and outlet connector from the old unit to thread into the new unit! I searched for the proper connector and could not find one and there was no explanation of why I was having this problem. There was no info on the Pentair web site about the type of threads on the inlet and outlet for either models. What I learned was that the inlet/outlet on the ASTM are brass and are threaded for "V" type pipe connector (NPT tight thread) where as the Mastertemp 250HD connectors use a buttress thread (aka., flat thread) (google>" Pentair 77707-0017 Connector Tube"). So to connect the pool heater to the pool piping, I just bought single a 2" OD x 12"long NPT threaded on both ends CPVC (not PVC) pipe nipple connector and cut it in half, then I screwed one of the halves into the threaded pool water inlet and the other half into the outlet, then I just glued the cut ends like regular PVC pipe to the pool piping. The pool water inlet and outlet on this heater are brass (not black), which outlasts most Pentair models. My old model's copper heating tubes corroded in 2 years, covered my warranty, but then the fire box corroded a year later!
(UPC #788379858278 Sku PUR-15-0779)
I replaced my Pentair Mastertemp 250HD with a slightly used ($1500) Pentair Mastertemp 400HD model 461021 ASTM, an exact fit so it would be an easy install. However. I could not get the pool water inlet and outlet connector from the old unit to thread into the new unit! I searched for the proper connector and could not find one and there was no explanation of why I was having this problem. There was no info on the Pentair web site about the type of threads on the inlet and outlet for either models. What I learned was that the inlet/outlet on the ASTM are brass and are threaded for "V" type pipe connector (NPT tight thread) where as the Mastertemp 250HD connectors use a buttress thread (aka., flat thread) (google>" Pentair 77707-0017 Connector Tube"). So to connect the pool heater to the pool piping, I just bought single a 2" OD x 12"long NPT threaded on both ends CPVC (not PVC) pipe nipple connector and cut it in half, then I screwed one of the halves into the threaded pool water inlet and the other half into the outlet, then I just glued the cut ends like regular PVC pipe to the pool piping. The pool water inlet and outlet on this heater are brass (not black), which outlasts most Pentair models. My old model's copper heating tubes corroded in 2 years, covered my warranty, but then the fire box corroded a year later!
(UPC #788379858278 Sku PUR-15-0779)
