I have a Worcester Greenstar 24Ri that constantly runs?

Why does it keep running? British Gas inspected it and said that it works from a thermostat and if the temperature drops below 7 degrees than it will fire up. This stops the boiler from feezing, so they said. All well and good but it is 10 degrees outside and the boiler is still running and seems to be heating the radiator in the donwstairs toilet. Very hot in there. Also when it was 20 degrees outside my boiler was still running and my downstairs radiator still blasted out heat.

Can anyone help please.