Why does my Boiler fire up when timed to be Off?

Help! I have a Digistat RF3 Transmitter and SCR receiver. My problem is that my Boiler fires up when timed to be off and has even done so in 'Holiday' mode when the entire system is supposed to shut down. It comes on and goes off ok when timed to do so (e.g. 1600-2100hrs) but then comes on and goes off intermittently when it is supposed to be inactive. I have put new batteries in the RF3 and done the recommissioning process which seems to have gone ok - Red and green lights came on in sequence with audible 'click' - but something is obviously still wrong. Any ideas please?