Potterton Prima overheating & locking out

[Cjelectrics]

Boiler is locking out after around 2 hours of being on, checked pump & valve & wiring & drained system, flushed pipes no blockage . Pump & 3 port valve are only 2 year old.
I'm an electrician and can wire central heating & take the controls apart but not trained on the pipes.
I've had the head off the pump & found some lagging caught inside so I cleaned that out , drained the system & few times between pumping the water around to flush out any dirt - all clean, radiators aren't patchy either.

Does anyone know about the 2 or 3 stats inside the boiler that may be playing up and causing the boiler to overheat & lock out sometimes or at other times just turn off before it reaches target temperature but NOT lock out?

I can't think of anything else except that the pump has had it, I got told to see how much force it take to stop the pump spinning with a screwdriver, they said it should take a lot of force but I was able to stop it spinning with a 4mm flat blade and just 1 hand pushing against the propeller.

Any suggestion on what to check or questions for me about the system & what I have done would be greatly appreciated.

Many Thanks

 

[Atouchofgas]

If you were able to stop the pump, it's had it

 

[Frog67]

Sounds like the pumps had it. Lagging inside the pump? oh dear!, if that's got round the rest of the system you may start getting circulation problems. If any has entered the boilers heat exchanger then this would cause it to lock out due to the waterways being blocked.
Check the expansion tank for debris as this is the most likeliest place that lagging would have entered the system.