Hi, the last two years I have used the RT500RF. I have always had the settings set at 5deg, then when I want the central heating on I would increase the temp above the 5 deg. ie room temp 16 deg scroll up to say 20deg the heating would come on. My problem started today, the heating just turns itself on all day today, even though as I say it is set at 5 deg. how can this happen. the only way to stop it comming on, is to turn off the reciever on the wall. please help?