David - The cause of the non-flow of the return to the expansion type solved. The 4-way connector has a reduction vavle , mine was in the incorrect pipe. It was in the engine rail to 4-way instead of the 4-way heater pipe outlet. Swopped over and not have a return feed.
I think it may have been assembled incorrectly, as the 4-way connector and pipes are supplied as one unit!