How can I fix my Glow Worm Space Saver 38?

Hi can anyone help...my boiler keeps going out, even when fired up. When it goes out it can be really difficult to light again. I have been told that it may be the Thermocouple....does this sound correct, if so can anyone advise me what the part number is. I have looked on keeptheheaton.com and there are number listed
Many Thanks.....a very COLD Cat