618

My Vaillant ecoTEC plus 618 display is always illuminated - previously it would go dark until I turned one of the temperature setting knobs. Not only that but now the temperature shown is flickering irregularly around the preset temperature (70°) and also flashing back to the outgoing...

Firstly, I'm not going to attempt to do any rewiring my self - but I do have a Gas Safe plumber on the job currently (waiting for an internal pipe that is leaking a bit), and I want to get informed on our situation so when he comes back we can get it sorted asap. I have a Y plan heating setup...