Drayton Rf2 digital wireless unit going haywire?

Hi all, have had probs with this unit a couple of yrs ago and had to reset the thermostat to the scr but came home tonight to find the o/half irate, no heat at all, temp on thermo said 5 degrees and totally unable to push it up to a proper setting, each time i get it to about 19 degrees it flies down to 5 deg again, went into loft to press manual setting, removed batteries till thermo screen went blank, replaced in correct order and it went to 5 degrees again and in the process shut off the manual, will try again on removing batteries but feel theres an underlying issue, Anyone got any ideas

Cold in scotland :-(