Did a complete heater hose renewal 6 months ago. Basically changed all heater hoses and after the renewal i did not have any heat. I checked the valve and pump and both where fine. I flushed the heater matrix and it was super clean. Checked the fuses responsible for heating and ac and all where good. I was so puzzled. Finally had a read of the workshop manual and checked the heater core diagram and saw the non return valve hoses with the correct coolant flow directions.... i had placed the heater pump non return valve hose in the opposite way hence no coolant reached the heater pump.... !! Found this after 6 months!!
Wanted to share this with you because i think its easy to mess with this when replacing this hose and its a pain to identify the cause of no heat.. could lead to unnecessary expenses such as replacing pump and valve...
I am attaching here photos of the diagrams showing the correct flow directions. and the picture of the non return valve hose which i messed and placed in the opposite way.

 

Well....that was not easy to find, I would guess. Due diligence has certainly paid off
in your case. I am glad you can get some heat in that Jaguar.

 

It's something I learnt to remove in one piece, I've also learnt something new in the above diagram, there's 2 of the blighters - 5 & 9, just to make things even more confusing!
Well done on the fix. They've got good heat....unless the blowers are blocked with foam!