Glowworm Xtrafast No Gas

I have a Glowworm Xtrafast 120 Combi Boiler and keep getting the "no gas" symbol flashing when I turn on the hot tap. after several turn off/on attempts it goes and everythings ok. I've recently had my Meter Housing moved and have had to reconnect the Meter to the internal gas pipe so i am wondering if this has anything to do with it ? A friend told me that soldering the pipe joints may have caused some dirty deposits on a filter in the boiler ? I don't know much about these and wondered if this was right and if so, where is it ? is it easy to do ? (The boiler is under 12 mnths old and was fitted by a corgi fitter but i can't find his details at the moment and don't know if Gloworm will come and look ? Hope someone can help.