Diagnosis Myson Orion 40si boiler misbehaving...please

[Mike58]

Our trusty old Myson Orion 40si has been misbehaving recently and now has thrown its toys out the pram.
I'm looking for advice from this symptom. ( not using CH much right now)
Ask for hot water, boiler will fire up from cold, run for about 2.5 mins then shut down. Won't fire up again until cold.
Got a heating engineer in for 15 min , tried to sell me new boiler and had no interest in diagnosing the fault, said the fan sounded suspect so I removed it and the impeller is running smoothly so doubt it's that ( but what do I know !!)
So I'm looking for advice re this sort of behaviour , it seemed to be intermittent a month ago but now this is the situation, fires up, stops, won't retire until cold.

 

[ShaunCorbs]

sorry to say put everything back together and stop messing inside as your not gas safe registered

have you looked at the pump?

 

[Burger]

Agree with @ShaunCorbs with leaving your boiler alone as not being gas safe registered. Have you checked the programmer, pump, cylinder thermostat, zone valve? Have you got hot water and it’s actually to temperature and doing it’s job?

 

[Matthew22]

Sludge

 

[Stu-B]

Flow issue causing overheat look at the pump first

 

[Mike58]

Thanks for the quick replies
Yep I am not gas registered , so no way will I interfere with the gas side of the boiler, but removing two 8mm nuts and a 5 pin plug to get the fan out is not rocket science .
First thing I did was suspect the pump, I'd fitted a Grundfos about 18 yr ago so replaced it with a newish Alpha 2 model when the problems started.
Is it likely the gas valve solenoids are faulty?

 

[ShaunCorbs]

closed

 

[Harvest Fields]

Agree with @ShaunCorbs above. You are blatantly ignoring the advice above.