Siemens rcr10/433 how to restart it?

My central heating stopped working but boiler and transmitting unit both seem fine and still have hot water. The receiver unit has no green light at all. Followed every instruction I can find such as pressing the set button on the receiver and learn button on the transmitter but it just isn't responding. The advice I read tells you what a flashing green light means and an amber light but not what it means when there is no light whatsoever? The people who fit the boiler couldn't give much advice, the boiler manufacturer say its not there problem so what can I do now?!