[captcolour]

Update: The plastic pipe and fittings are PEX. Bought a brass female fitting for the pipe, and the Pex clamps, and of course a pretty expensive Pex crimping tool. Well I guess now I have one. Put it back together, filled the tank, and turned the electric heater on. Checked it a few hours later and we have very hot, hot water flowing. There was much rejoicing.



So check valve was the problem and we now have a spare.