Camray 5 Oil Boiler fan will not stop?

Our combi heater and water oil boiler Camray 5 does not stop the fan when the system turns off. Normally when we turn the heating to off and water off the unit switches off and the flue fan stops. It now stays on and the only way to stop it is to turn the power off. Is this a control box fault, control cable connection fault,? We have had work done on the pulmbing in the last few weeks with the boiler on/off several times and systems drained etc. Something may have been disturbed?
Never liked the control box being inside the sound proof housing, maybe a new controller on the outside?