Vokera Mynute 16e shutting off (burner going out)

[distantstorm]

I've noticed my radiators not staying hot recently. Having not really paid it much attention I ventured out to garage and looked at boiler today - noticed pressure was 0.4 bar and thought I had sussed problem (I confess I've not looked at the pressure in the last 2 and a half years). I topped it up, pressure is at 1.5 bar now. But when I turn on heating it will stay on for anything between twenty minutes and an hour and a half before the radiators go cold again. When I go out the light indicating flame is out is flashing away and I have to reset the boiler. It then fires up and lasts 20 min to 1.5 hours again.

I've been looking at forum and other sites and seem to have come up with thermistor or PCB, either of which I am willing to swap out myself. There's not much mentioned about the high limit thermostat though so my question is.. am I barking up the right or wrong tree and if I replace thermistor am I as well doing the high limit thermostat at the same time? Obviously given the cost I'd rather try either/both these options before PCB but only if I've got the right idea!

Oh, boiler is about 3 and a half years old. Thanks for any advice.

Update - just turned heating on in house again and boiler tried to start up but almost immediately went to flashing "no flame" again and required resetting twice before burner would start. Not sure if relevant but thought I better add in the extra info. Thanks

 

[nickso]

pcb's can cause that fault but so can a lot of other things.

i personally would go for the pcb simply from previous experience but its a guess and you have to be prepared for the reality that throwing parts at a problem without diagnosing it right may cost money and leave you with a lot of spares. sometimes of course you cant diagnose properly and have to go for the most likely component.