My Potterton EP2000 needs to be replace (display faulty). Is there: 1) a direct replacement (that requires no re-wiring). That is, it plugs directly into the existing back plate? 2) a replacement that requires slight wiring. If so, does the back plate require replacing or just re-wiring of the existing back plate? Ideally I would like something from B& Q or Wickes (less than £50.00). Thanks.