Danfoss TP5000RF not working properly

I purchased a Danfoss TP5000RF and single channel reciever about 18 months ago. It has worked OK until now.
I have the heating allways on via the CH/HW timer (just set to cont. instead of timed) and the TP5000RF is programmed to set the temp (in the living room) to 23 deg. at 6am. This appears to happen OK and when I make it downstairs at about 7am the temp is on its way up. The problem is on the switch off. It doesnt register the fact that the room is up to temp. and therefor doesnt switch off the heating. If I get SWMBO to press the manual temp overide buttons (up and down) and I check the reciever, the green light (which indicactes that it has recieved a signal) doesnt light up. I have to take the TP5000RF off the wall and take it to the reciever and press the buttons to get it to register that its up to temp.
This is odd because I guess the signal to tell the system that its too cold at 6am must be getting through because the heating comes on. Its just the signal to tell the system that its hot enought.
I have tried powering off the reciever, removing the batteries until the LCD clears and re-synching and programming everything, but it still doesnt work.
I havent made any mods to the house that would be blocking the signal. As I mentioned above the 'switch on' signal is getting through.
Any ideas on how to progress this ? I dont really want to throw the equipement as its only 18 months old and cost over 100 pounds.
I guess hardwired stuff is a bit easier to fault find. At least you can see the wires !

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