When you pressed the pair button on the adapter, did the top light blink? If not, better press and hold the pair button longer, for about 10 seconds, on both adapters. Then press the pair button again for 1 sec to pair them. You can also use the utility to pair them. Reset them through the utility may help.

Thanks for coming back to me. The answer is no, it does not blink. When I try the 10 sec reset.... for a split second all three light up then immediately it goes back to the top and bottom lit up, middle light off. The bottom light occasionally blinks.
I have 6 adapters around my house, there were all working fine, so should I unplug each and everyone of them until I get one working then add all the others? I was wondering if one of the is the cause of the problem? The other thing Is, is I cannot seem to 're pair' any up.... I have one in the kitchen that is easily accessible, and for that I have tried the 10 sec restart then pairing but as I mentioned above, nothing happens. The line is still dead.

Yes better pair one by one. And try the 1 second pair after the 10 second pair. You can follow the video http://www.tp-link.com/en/download/TL-WPA4226KIT.html

Thanks - I am all sorted - I downloaded the utility, reset them all and it has worked. Thanks for your help!