Hot Water Heat Piping Schematic

[KevinE]

I am having issues with my hot water not heating properly, even after 4 hours of motoring (I had the boat yard replace some rotten lines, never worked properly after that).

My system is as follows
I have an ardic diesel heater in the aft lazerette plumbed into my freshwater engine cooling loop. The system uses a heat exchanger to provide forced air heating in the cabin. The heat exchanger is installed below the port settee.
The hot water tank is installed forward of the heat exchanger under the port settee also.

The proper route for the piping then is diesel heater -> engine -> hot water tank -> ardic heat exchanger -> diesel heater right?

Now with cold coolant, the thermostat on the engine should be closed so flow would be prevented through the engine so a bypass line is required (if I want to use the ardic to heat water and provide cabin heat). If you do this then I think you need a one way valve in the bypass line to make sure the engine doesn't just cycle the coolant on itself.

This is my thinking on the system but it just doesn't work. Does anybody have a schematic that I could double check my arrangement against?