Aussie,
I took off the top engine hose and established that is DOES have a Thremostat and it was closed, when cold.
Disconnected the heater hoses, connected the garden hose and switched controls in all directions, changed hose inputs and alas! no flow thru.
This leads me to the conclusion thats its a rooted tap or the driver control panel connections.
I have no way of fault finding these connections as I dont have a wiring diagram I I thing the Installers are adapting one from a different model