Help for my plumber still wanted - Please!

[the ink monitor]

I have an approx. 5 year old Potterton Kingfisher Mf (CFL100) that has developed a very intermittent fault which causes it to cut out. It has been serviced regularly by a fully qualified engineer and he is loath (for cost reasons) to start replacing various bits when we are not sure exactly what is wrong.
It will go for weeks working perfectly well and then cut out. I push the reset button and it will spring immediately to life and run again for maybe a day, a week, a month – there is no pattern to it and then inexplicably, for no reason at all, cut out again, and so the cycle starts all over again.

Can anyone pin point the fault please?

 

[Puddle]

Sorry ink monitor we are not ignoring you, its just that your plumber is right when he says you can not just going replacing bits in the hope you will hit the problem, parts are to expensive and as boiler so old and not that common, the parts purchased would probably not be able to be used else were
I know intermittent faults are infuriating and they seem to becoming more common as build quality goes down. However if your boiler works perfect for as long as a month, then you can imagine how many times it is going on and off with no problem
If it has been serviced regularly then presume burner, electrodes, sensors ok
On this boiler, there are not a few common faults, so we could say from experience it would either this of that
When they first came out ,we had a lot of problems with gas valve sticking, coil burning out and damaging pcb,both had to be replaced, you can imagine the cost of that, air pressure switches also have been a problem ,this could be replaced as could be used else were if problem persists
So you are probably going to have to wait until problem gets worse, so fault can be seen
Few things to check would be to make sure the fan drum blades are clean ,removing any build up ,also that the appliance earthing is sound
Try and see when it is going to reset, is it when appliance is on or at start up
One thing I would add you are hitting the 5 or 6 year potterton itch with their PCB boards, often their boilers develop dry/cracked joints on the boards. So it could be a good idea to have removed and resolder main connections

 

[the ink monitor]

Thank you for your helpful reply 'puddle' - as I am in the AV industry myself and dry joints are a regular problem with older equipment, so might try that with the PCB (on advice from my plumber, of course!)
5 year old boiler, old, though??!!?? My goodness what happened to the 'good old days' when equipment lasted? This boiler replaced an at least 20 year old gas converted from oil boiler that was a perforated as a tea strainer but it still worked!

Sorry - just noticed something you asked (that'll teach me for being too quick off the mark)

"is it when appliance is on or at start up"

Always at start up - once it's up and running there is no problem...............
......would that possibly pin point something? (hope so!)

 

[GroundControl]

no help but a worthy comment is as you know electronics can be very fickle especially intermittents !!! and of course the EU dictates the an appliance only has to be repairable for 10 years as technology advances they want you to keep up with the higher efficiences and methods. and most of all you cant fix it if it aint broke ----sorry

 

[Puddle]

Well if happening at start up ,I would be drawn towards sticking gas valve, not opening in time required, causing boiler to go to lock out or as said pcb with dry joints causing flame not to be recognized in time and then causing lock out,also check flame detection sensor distance is correct on burner as over period in time can bend away slightly
So I would first of all get PCB main connections and relay connections re soldered
And see how you get on

 

[the ink monitor]

Thank you puddle and very much appreciated - I promise to get back to you when (and if!) I solve it via your advice.