Siemens RCR10/433-GB Receiver Keeps Sticking?

Having read some of these threads, it appears that there is a common problem with the receiver I have with my mobile thermostat. It dos work it you give it a couple of taps on the top when heating is called for, but then the next time it is due to come on, you have to do it again.

Anyone have any solve issues for a sticking relay etc on this type of receiver? I have only had it for 3 years is it on its way out and I need a new one?Thanks