In reply to aln:
> My flat has radiators running off the combi boiler, controlled by a thermostat in the hall, opposite a radiator which is permanently on. If I want to stop my pipes freezing when I'm out, will this one radiator be enough to do that. Or do I have to have them all turned on?
Check you boiler manual. I think most have an frost-stat built in that will prevent the pipes/radiators freezing.
> Also, when I'm at home and trying to stay warm while using as little fuel as possible, my instinct is to have all the internal doors closed, use draught excluders et. Yet last year when the system was getting an annual service, the gas man told me the system actually works more efficiently if the doors are left slightly ajar.
Sounds like an urban myth similar to you should have your heating on all day for more efficiency,.