I've got a Glowworm Economy plus 60 F boiler fitted in 2001. It was o.k. at first but these last couple of years it's been noisy, with spitting and backfiring sounds. Lately I've replaced the fan and a few other bits, and yesterday I had it serviced and the whole system flushed and the pump, etc. replaced. The plumber who did the flushing was determined to find the problem as he was surprised that the flushing didn't seem to make much difference to the banging etc., so suggested I replace virtually everything which I did. He also suggested I exchange the right angled pipework in the loft for straight fitting pipes which might facilitate the boiler. This seemed to work at first and it was really quiet. The plumber left with quite a hefty cheque and we were both satisfied that the job was done. However, a few hours later, the clanging and backfiring sounds started again. All the radiators are now hot but as before there does seem to be a bit of air trapped somewhere which seems to build up. This has just cost me over £700 and it's still not working properly. The plumber hinted that it might make a difference if I were to raise the feed and expansion cistern a bit higher. He certainly was keen to find the problem but I am now at my wits end. Anybody got any ideas?