Could be the photocell to the combustion chamber is sooted up - easily pulled out, wiped and put back.
Could be the nozzel - check that it is clean, may need brushing with wire brush - check electrodes are clean and correctly positioned - you can download maintenance guidelines to get the exact dimensions (3mm apart and 1mm back from the nozzel end - from memory).
Could be the filter to the nozzel is blocked - can be cleaned but a replacement is better - get one with the same numbers on it - or take it to your local watch repairer to go in his ultrasonic cleaning gizmo - they work a treat.
Mine kept locking out and after I'd paid an engineer £300 to put a new motor in, which didn't change anything, I eventually found the wires to the electrodes on the nozzel had corroded - some electrical tape did the trick.
I tamper around with mine if I get any problems, once you get used to taking these apart they are quite simple to understand and safe (I think!) remember to turn off the power if your poking around near the electrical parts and best to turn off the oil tap if your taking nozzels out etc.
Dan Rack, January 2009
