I have a Honeywell CF wall mounted programmable thermostat thats gone rouge?

My programmer seems to have a mind of its own. It is switching the heating on much earlier than the programmed start times and even switching it on at random times if I leave it on the 'auto setting' I have tried reprogramming it, checking the selected room temperature, re bonding it after clearing all preset programs, new batteries etc etc but it still seems to have a mind of its own. The boiler has recently been fixed and had a new circuit board but this was happening before that so cannot be connected. Its only 4 years old and the boiler chap said they rarely go wrong. Any ideas or is it time to bin it and get a new one.??