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              It's getting cold... how are you going to keep heating costs low this winter?
 
            
            (piefed.blahaj.zone)
          
          Community for asking and answering any question related to the life, the people or anything related to the UK.
Hope you have a smart thermostat and smart radiator valves, and close doors between rooms. It'll only have the boiler on when rooms need it, and unused rooms can be left at 10 or 12 degrees until you need them.
Heating a whole house to 18 degrees isn't efficient, but also this may help you isolate the problem if you find that with certain rooms closed off you're not losing heat in the same way.
Edit: also if you have UPVC doors, they have a summer and winter setting. The summer setting leaves an air gap to allow better airflow out for ventilation, but obviously that's the worst idea in winter. I adjust my doors with each season - there are YouTube videos on how to do it. It's literally just turning an alan key to loosen the lock gap.