im guessing you have a combi boiler... if so i should imagine that you have a faulty diverter valve. (this i understand is an electronic valve which opens as you make a demand for the heating) if the valve is failing then the boiler in return will have nothing to fire up for. I am not however, technical in the world of the lovely boiler.. but it does sound very similar to a problem i experienced a short while ago.
hope you get it sorted, and at worst you may be cold.... but at least you wont smell! good luck
danny
October 2009