I have oil central heating which has been working great for the past few years. In the last few weeks the problem i am having is that when the heating goes off at night the radiators get cold within 20 minutes. Also the copper tank which wiould have half a tank of hot water would be freezing when i got up in the morning. i have checked for leaks everywhere and can not find any both inside and outside leading to the boiler. I have also had the boiler serviced two weeks ago and the heating is the same. The lad that serviced the boiler said that the boiler is in good condition and there is no problems with it.