Can't get Siemens RDJ10RF thermostat to reset?

Had no problem with the fitting on wall next to boiler but when I press "learn" on the other part to get two pieces to communicate absolutely nothing happens. Is there any way I can get my heating to work without the thermostat communicating or any other suggestions for making it communicate. Similarly if I press the test button nothing happens. I have put in new batteries. Could this part just need replacing?