so ive changed my HCV twice now as I was intermittent getting hot air while the dial was set as cold. The 1st one I installed was faulty as I got hot air even when set as cold. Now on the 2nd one where now I dont get hot air at all. Another faulty HCV ? I've flushed through the 2 heater matrix hoses at the bulkhead to make sure its not blocked and water runs through fine.  On 2 occasions it did get hot air, but once I turn the dial back to cold and back to hot it doesnt get hot anymore. The 2 front facing hoses are hot, I did feel the 2 rear ones they were warmish but not as hot as the 2 fronts. If the 2 rear hoses of the hcv are hot does that means its letting the hot water into the water maxtrix right ? Any ideas here ? 

so it appears the 2nd HCV was faulty as well  this was a EIS brand from ECP. I ordered a blueprint one and they use the latest revision 7N21 18495-AB which has solved the issue. Ford does not make this part anymore.

Your story is pretty much identical to mine. Exactly the same issue from a pattern part. Now on my fifth unit after the last pattern item lasted just four weeks. Done all the same coolant flush and changes. Clearly saw coolant ingress past the rubber seal which led to failure. I did see a genuine new Ford item for £105!! but actually went for a Borg & Beck a couple of weeks ago. So far, so good but I would not be surprised if I am replacing again some time. As winter is approaching I am not so worried if it fails and stays on hot until spring.