The small temperature thermocouple which has a geen plug on it with two yellow wires has failed or has been tightened up too much because it may have been leaking. It has a fibre washer on it which is crap, and when it is tightened up too much it twists the internall parts so it cant latch properly. Everything works on the boiler but it just wont ignite, its a bugger.
monty
May 2010
Your over heat stat has failed. Its the one attached to the copper pipe on the left hand side on a little square plate.
Dune
April 2010
had the same problem this week the white star seals when u put the inner casing on this causes it to vacum bringing the preasure switck into play cheak ur seals also cheak the wires to the preasure switch hope this helps but make sure ur inner casing is on correctly its a sh*t
billy
April 2009
how far through ignition does it go, can you hear the boiler sparking