Digistat+ intermitant communication?

Hi, I've had a digistat+ for 3 years and it has worked fine, but recently it has been failing to work intermitantly. The green light is on the receiver but the heating doesn't start. If I knock the power supply off and then back on, it works for a week or so and then just stops and I have to knock it off and on again. Any ideas out there? Thanks in advance.