ocean alpha 240p combination boiler,i have a ten year old boiler and every time it gets cold and the demand on the boiler is higher than normal both my hot water and central heating don't work,by that i mean everything comes on as normal ie all the electrical functions work but the red light comes on and the boiler doesn't light and the pilot is lit,now after say a couple of hours with the timer still active the boiler fires up!! help!could it be the little temperature sensor fitted into the output end of the central heating feed pipe?