Recently, in damp cold weather boiler fails to fire up in the morning, used the reset option and all was fine but wondered why it kept happening. Knew of issues with condensation pipes so checked them and they were clear, decided to check syphon tank that feeds condensation pipe, necessitates removing front cover, 2 screws at top, 2 angled at bottom, bottom plate 2 screws, electric control unit 2 screws either side, and this allowed access to syphon bracket, 2 screws to removed bracket and allow syphon tank to be removed, twist and pull down. It has a rubber o ring on the drain pipe at the top that seals the tank to the boiler, just twist and pull down, noticed that tank was full of grey gunk and bits of gritty sh*te, cleaned it out and realized that the cause of the lockouts was that the condensation water could not drain away quick enough so backed up and shut boiler down, after a while it managed to slowly drain to allow system to be fired up again until syphon tank clogged up again. Worth considering if you are having problems and your condensing pipe is clear.
Simples (and no cost)
Al, March 2017