Superstor marine SS12M heater problem

by Neil McCubbin
(Canada)

I have had the Superstor marine SS12M heater operating satisfactorily in a sailboat since 2004, except for one significant problem.

It does not drain until empty when laying up for winter. The piping is installed as the manual, with a 1/2" drain valve in a tee pointing downwards on the cold water inlet.

When new, the heater leaked after the first winter, because it had not drained dry, despite the drain valve being open and the hot water taps and a vent in the hot water line being open.

Superstor replaced the unit under warranty.
Since then, I have filled the heater with anti-freeze in the winter. However, the non-toxic "plumbers" antifreeze is not available where the boat is now located in the UK, so I really want to drain the unit, and be SURE that it is drained.

Is the drain connection inside the tank right at the bottom?

Any ideas on how to drain it and be sure it is empty?

(the water heating coil is not a problem, since the engine cooling cricuit has antifreeze in it)

Thanks