In our house a couple of the rads will heat up fine when the heat first comes on, then will go off after about an hour and might stay off for a couple of hours even when turned up to high. They might come on again at some stage and then go off again. Is this related to the temp control, the thermostat is set to 25 degrees. The boiler temp goes up and down between 53 and 70 c approx depending (gas), and there is one timer for the boiler and one for the rads which are synronised manually so they are on at the same times. One of the ones that keeps going off is in the sitting room which is the problem. There are 3 that go off the others will be boiling hot more or less constantly. Would increasing the temp on the thermostat fix it?