Blt Egr/asv draining battery

Hi, I have a Blt engined fabia vrs. Twice now I have gone to use the car and be unable to start it. Once the battery has been recharged, new 6 months ago, I can hear the electronic part of this system 'humming' away. Once this has be disconnected the humming stops. I have had the system stripped and cleaned which sorted it for 4 months or so but has started again. Any advice would be appreciated. Is a replacement the next step, or more likley a faulty sender controlling it?