Pauline, we have had similar trouble. Just managed to get ours working. Try resetting the Controller (or transmitter - where you set temperature) you do this by pressing the TEST and LEARN buttons together. Then press SET on the device connected to the Boiler (receiver) and the LEARN on the controller/transmitter, then when the Green light starts to flash on the Receiver (at the Boiler) press the TEST button on the controller. Hope this works. This is only a temporary fix...if this keeps happening regularly you should get the unit checked.
Steve & Sam
January 2009