Worcester 26/32 Oil-fired boiler - intermittent lockout

The Worcester 26/32 Heatslave boiler broke on Boxing Day with following symptoms (diagnosed by engineer) and happened at the same time.

Leaking flow switch caused water to wick through sheath and spill over PCB and boiler overheat stat - both went bang
Expansion chamber diaphragm ruptured - confirmed with water at Schrader valve
Burner chuffing with lock out

Rectified defects and replaced photocell and all burner pressure, air valve and CO settings correct and worked OK for a few hours.
However, burner now intermittently locks out (especially when warm) and needs resetting. Just today, I noticed that the lockout light on face of cabinet goes out without having been reset but comes on if demand made on boiler (and obviusly no results heatwise).
Could the controller - a Satronic TF 832.3 - be the cause? It has a PCB and I wonder if radiated heat is causing the intermittent fault.
Engineer is a top bloke and spent all Saturday afternoon here. Fault happened once after all back together - reset - could not reproduce but has happened twice today. As I write, boiler is happy with no heating demand and occasional demand for hot water with no problem. Soon, with heating on, I expect problems.
The long and short of the requests is: has any of you seen similar and what was the cure?

VLSI?? surface mount, yes but it's nowhere near VLSI. Possible control box, but also photocell, though more likely is solenoid coil. However, we aren't in front of the boiler so your top bloke is the best option.

Oilman - thanks very much for response; I'll correct my error concerning the configuration of the PCB.

I suggest you put your error back, otherwise it makes no sense.

Lockout light on facia only illuminates when demand on burner as it takes it's power from the control box on burner.
Without being in front of boiler it is hard to diagnose, but would start with solenoid on oil pump as it is allot cheaper than a control box.