Glow worm 35F Main burner won't stay lit

[ottosump]

Hello group, I have been having a spot of bother recently with a glow worm 35f fuel saver boiler, it developed a fault a few weeks ago which I rectified with a new Randal 103 timer, the boiler ran for a fortnight with no issues. A couple of days ago I noticed that the main burner had gone out, the pilot was lit, and the ignition was sparking constantly. When it was turned off and left to cool it would restart, the main burner would run for approx 30 seconds then go off. The pilot was lit and the spark was firing, I cleaned the boiler out, WD40'd the fan assembly, the boiler started again with the main burn, the main burn went out, lit again and cycled few times like this, I did notice that the pilot was sometimes going out then re-lighting again. Any ideas group, its a positive pressure type boiler, all appears well inside the unit.
Regards Otto

 

[45yearsagasman]

Firstly, fitting a 103 timer would not have cured a boiler fault as its an external control.
You are correct about the case being positive pressure and as such are inherently more dangerous if worked on by a non competent person.
The fault you describe is fairly simple to fix but should really only be undertaken by RGI's.

 

[ottosump]

Thanks gas man, the problem I was experiencing with regards to changing the timer was not connected with this fault, the fault on that occasion was the fuse in the spur was tripping, the replacement timer rectified that fault, sorry for the confusion.
Could you shed a little light on the fix for the problem I am currently experiencing?
Regards Otto

 

[ottosump]

Was informed by an ex installer that the problem could be the gas valve solenoid, which one will be at fault, there are x2 on this model?
Regards Otto

 

[mickyg]

you wont get any further advice on this forum as it discourages diy gas work. employ a competent rgi and it should be a relatatively straight forward fix.

 

[ottosump]

Quick update, managed to get a registered installer to check the boiler out, he said it was the PCB and it would cost £135+ VAT fitted. This I paid and the unit was OK. Now I'm back to square one, it is doing exactly the same, got the same company to come out as I told them the PCB must be under warranty, another engineer came out and informed me that the new fault is nothing to do with the replacement PCB, I stressed that it is the EXACT same fault, but no, he reckons its a pressure switch, £70+VAT fitted, and he will give me 12 months warranty on it?
I feel slightly ripped off !
Otto