It strikes me that this has nothing to do with central heating per se but is most likely to point to an increased release within (only) your home of vapours of some type as the temperature rises - which will then also happen during the few days of warm weather to be expected during July and August.
If you have added anything, particularly containing any type of synthetic material, to your home's collection of furniture, carpets, etc. or painted something there sometime immediately before this started happening then that could be the culprit. Obviously, you will want to find what is causing this because you won't want to be living in a house so cold that it is not truly fit to live in.