Worcester 19/25 fuel oil lock out switch blown

[Lin G]

Hello what fun I’ve had tonight.
I have an elderly boiler as above but it’s been visited a few times and has lots of shiny bits on, just like Triggers broom.
The lock out switch came on (not seen since last winter) so I took the main cover off and then the lock out switch cover and performed the ‘switch off at mains, press reset, switch back on again’ procedure. Worked fir about five mins then stopped again. Turned off hot water heater and tried it again. Turned off CH and tried it, then turned CH on and it still locked out.
Lots of fuel oil so no issues there.
Pressure is always low to start with then leaps up to 2 when heating or water on.
Last time I tried the reset the unit that you press blew and fused the ring main.
That’s all sorted now (lights back on) but now... what to do?

 

[oilboffin]

What burner has it got

 

[Lin G]

I have no idea? Just the one supplied. I changed the control box (containing the lock out switch) and changed a fuse. Seems ok now but wondering where condensation inside the control box came from

 

[oilboffin]

Just general damp.Bob

 

[oilhead]

Is this an external boiler? If so this could explain the condensation in the control box. It also sounds as though you need to get the expansion vessel sorted out if pressure fluctuates wildly.