Display gone on Digistat RF2 Wireless Thermostat?

Hi...wonder if anyone can help please? Been driven mad after the display on the thermostat went making the red alarm on the receiver flash. Changed the batteries & came on again only for a while. After 2 lots of batteries, realised that wasnt the answer & went online. People were saying the batteries were loose & suggested using foil to mend connections. Did that today & it worked for a while but you could see the display gradually fading until it went off again altogether. Common sense makes me think its the thermostat because there is no display? If it was the receiver that was faulty, surely we would have a display on the stat but no heating?
Would really appreciate any help. Many thanks :)