At some point, MMC must have removed the on / off water valve. My heater matrix is permanently fed with hot water and there is simply a flap to stop the hot air coming into the car.
I'm going to add a valve so I can turn it off in hot weather as a bit of the hot air always finds it's way past the flap even in the off position.
That is exactly what I thought when posting this.
http://www.talkmorgan.com/ubbthreads.php/topics/600215/re-4-4-heater-not-heating#Post600215
