Rinnai HJ Cooper water heating element size

benbuc

I wish to insert a 1Kw element in middle of cylinder 250 liter tank (duplex stainless 2-3 years old.). It is blanked at the moment with castellated nut holding blanking disk. Hole appears to be 1.75 BSP (cylinder is in use so can't measure accurately). Rinnai only supply 2 and 3 Kw elements. Not sure if nut will clear top of threaded orifice to compress gasket washer. So I am trying to locate a suitable element 1.75 BSP and a long enough thread to tighten on gasket.
This element will be supplied by pv panels. Evacuated tube collector with controller is plumbed to bottom of cylinder.
Any help/ideas appreciated.

Jack

I am assuming that you are in Australia/NZ. Rinnai North America currently does not do electric units.