How can i fix my potterton kingfisher bolier?

Please help! My boiler is heating the water but no heat is going through to the radiators.I have been told that the motorised valve is not working.Is it true that the all kingfishers have a valve because i have looked everywhere under floorboards in my bathroom,kitchen etc.I have checked the thermostat and all radiators in the house,but nothing.If there is a motorised valve where would it be positioned?
Please help anyone i'm desperate!!!!