If your heating feed and expansion tank F&E looks like this, your heating system has not been checked when you had your boiler serviced. Call a registered plumber that's CORGI registered he will advise you what needs doing and a price or you can do as the owner of this property, he attached a hose to the overflow pipe running into the guttering. Now this could have been caused because Archimedes law was not given a chance.

,,,,,,,,and no I did not leave it like this!