I have a disconnected wire?

I have a wire come off my potterton netaheat boiler it was dislodged after it was serviced now the boiler wont fire the plumber has returned and said the boiler need replacing I would like to find where to put this wire just to see if it makes any difference and don't know where it goes. It is grey in colour and has a connector on it with a white wire with a spade on the end. The wire is coming down from the boiler towards the electronic panel but I can't see anywhere for the spade to go on the panel