Hi , I have a Worcester danesmoor 12/19 oil boiler which ran faultlessly for about 8 years then started to "lock out" intermittently. This was eventually traced to a faulty ht lead but only after most of the boiler innards were replaced. I has run now for a further 18 months but has started blowing fuses, I replace the fuse and away it goes again . Perhaps for a day or 2 days or even a week - then blows the fuse again. When it is running the lockout light is usually on (but not a lockout) but the boiler continues to run ?? My heating engineer is puzzled and because most of the guts were replaced 18 months ago cannot seem to find a cause.