I have one of these,SALUS RT500RF It is set to 5% over all the time settings, The sender unit works fine when I raise the temperature to turn the heating on 0k. and it turns it's self off when the room reaches the set temperature. But for quite some time the boiler will turn itself on ( central heating) quite at random, we may go 6 months with no trouble, then we may get a short run of days when it will turn itself on at random times. I have even tried taking the batteries out of the sender unit SALUS RT500RF and the boiler will still turn itself on when it likes.JUST TO SEE IF THE SENDER BOX IS AT FAULT So jumper settings don't even come into the problem as a cure. WHY DOES THIS KEEP HAPPENING.?? It has come on every day for the last 7 days, the longest run ever in 3 years. Thank you in advance Regards Neil

These are notorious for this its all down to the freqency any of your remotes could activate it even a passing taxi can activate it got this from Sallus tech. try altering the dip switches which will change the frequency tells you in the manual how to do this

Are you sure it is not in frost setting mode?