Thanks for all the replies.
I took the thermostat out and connected up a hose to the bottom hose connection and a waste pipe to the top and then reversed it and even with 3 bar of pressure nothing came out. Good point Arwyn on the impeller. I think I will have to drag the whole thing out, which is a bind.

Last edited by DavidA; 28/06/17 03:09 PM.