hi all i fitted the above room stat to my worcester 28si been working for last two weeks but lately ive noticed hearing like arcing sound from stat for a little while as it switches ,i didnt notice it when it was first fitted . its wired correctly using 0.75 flex , 3 wire connection as per instructions . i took stat case off to look what happens and i could see little arcs as the switch tried to seperate . QUESTION IS SHOULD THIS HAPPEN. i am thinking that perhaps this is not good for the boiler if its not switching correctly, is their a set time that it should take for it to switch?. any help most welcome paul