Sorry to dragg up an old thread, but I believe myself and my immediate neighbours (3 terraced town houses) have this issue as well on a 2004 Persimmon homes.
NHBC told me to do one, CWI not covered under their guarantee, and Persimmon I got an email with someone else copied in (wonder why) telling me to check for drafts and replace any door/window seals. Oh and maybe run my heating longer or get it set up correctly
No reply to my response.
Any advice how to get these clowns to fix their mess, AND refund me the increase heating costs?