I too had boiler fitted in 2005, a Worcester Greenstar 30 si, i also had it fitted in the attic. for the past 6 weeks wife and I have been up and down to our loft resetting it. sometimes up to 3 or 4 times a day. from the manual it was showing ignition lockout, would reset but would then lockout without any real pattern. On new years day refused to reset, so i took the cover off, knowing that i wouldn't get a plumber. When starting i could hear a gurgling noise from the flue, debris was also visible within the condensation trap. Taking the rubber pipe from the trap resulted in a significant amount of condensate (water) pouring down the rubber tubing from the bottom of the heat exchanger. Would appear that the condensate had not been draining properly. the condensate pipework we had fitted is 22mm but is not a weatherproof type and is susceptible to frost. the manual states that external pipework smaller than 32mm should be insulated. Tapping the pipework outside i could hear what sounded like stones i can only assume it was ice buildup. Inside i disconnected the condensate pipework and using a funnel, boiling water and a few good breaths blew it through. I also took the condensate trap off and gave it a good clean, rinsing it through. Easy enough and certainly not requiring the need of a plumber. My assumption is that because the condensate trap was clogged with debris the condensate has been trickling though rather than a larger quantity of condensate passing though after a syphoning action periodically. our typical british winters don't help. So far (24 hours) the boilers been working no problems, no resets and i actually think our water is running hotter.