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Can anyone help with this... I have a Worcester Bosch Heatslave 15/19. The boiler keeps going into lockout... However strangely, if it has been left for a long period it will run for a few minutes. Lockouts then reoccur, and in shorter and shorter periods. Eventually the boiler won't ignite and locks out straight away. I've bled the fuel pump, and tried bleeding the fuel line. There's a nice steady flow of oil to the pump (pulled from oil pump and run into a jar, steady flow no bubbles) and it pushes oil out when the pressure screw is backed off during bleeding (I don't have an oil pressure tool to test it though). Cleaned the photocell (which wasn't really dirty anyway) I thought perhaps the solenoid coil was the issue but it is magnetising to a screwdriver. I can hear the oil pump valve stem operating, when checked with a magnet. Pressure on the water gauge is also fine and you can hear the burner fan spinning nicely. Pulled the burner unit, no unburnt fuel in there... I haven't tried removing the fan to clean it, this didn't seem a likely cause if the fault to me. No settings have been changed e.g. burner, oil pump etc. It had a new burner nozzle about 2 years ago, haven't tried cleaning it through fear of damage... perhaps my next option? Any ideas before I book a specialist, I'm completely out of them? Thanks

I had a similar problem, I got in a local heating guy, he said not cost effective to test components, he simply changed one at a time and returned them to stock until fault found. Can't remember what it was in the end, but his method not really one which can be done DIY.

Hi stferr,
You could try removing the photocell and try starting the boiler, cover the cell during the initial part of the startup cycle, once the boiler has fired expose the cell to light. If the boiler keeps running you need to reinsert the photocell in slightly different positions and clean both sides of the swirl plate with a wire brush.
Regards S