potterton EP2000 (old brown one) problem - CH always on ???

I have a Potterton EP2000 - problem is when i try to put the HW slider on any setting i.e twice/ once/ 24hrs, the CH is coming on even though the CH slider is in the OFF position !! Is the problem with the control panel ? as even when i turned my wall thermostat in my hallway right down the radiators still got hot even though the CH setting on the Potterton control panel was in the OFF position ( but had the HW set at once/twice/ 24 hrs setting. ) Central Heating is only OFF if the HW switch is OFF. The boiler ( Potterton Netaheat Profile 50E) hasnt been in use for a long time as property has been empty for over 2 years. Please please advise if you can. Many thanks.