I'm off to Barcelona for a long weekend. At what temperature should I leave the CH thermostat in this kind of weather? My room stat goes all the way down to 5 degrees but that sounds too low to me. I just want to be sure the pipes don't freeze - the loft is insulated and the pipes are lagged and I'm happy to leave everything on 24h/24h but I don't want an enormous bill as a result. I'm thinking about 10 degrees.