Sabre/Vokera 24-28 HE combi. Only gets to ignition when inner case opened.

[casaco]

This boiler is driving me nuts, I have spent hours trying to sort it, cost me a fortune on the phone to vokera tech who to be honest seem to be quite hostile at times, (anyone else feel that way?)
The problem is everything works fine, pump runs, fan runs, APS works but no spark, open the combustion front, hey presto spark ignition, close combustion front no spark, fan and pump still running.
I have removed the fan and cleaned venturis, changed the APS, still the same, no blockage in the flue, fan running full strength. The tenant is behind with the rent so the landlord isn't interested, would like to get the heating back on for Christmas, she has a couple of young kids and hasn't had any heating or hot water for 6 months.
Has anyone any idea, am I missing the obvious?

 

[tipintim]

Air presure switch

 

[casaco]

No, fitted anew one, same result.

 

[Mbear]

Dirty fan Venturi. Aps tut tut tut

Always clean the Venturi first

 

[Mbear]

Sorry I misread ur post. My next port of call would be remove the flue restrictor. That should sort it mate

 

[tamz]

^^ if it is fitted

 

[Mbear]

Have the fan impeller blades been washed/cleaned aswell?

 

[casaco]

Took both venturis out, emery clothed them, spotless, now you can see why I am frustrated, the fan is really powerful and you can hear the APS click in, but no ignition til you open front of combustion box, Vokera tell me that it is definitely air flow problem, I have stripped it down 3 times and checked everything, but still can't get to ignition stage til front cover opened.

 

[casaco]

Not a mark on them, still look brand new, don't think she has used the boiler much since it was installed, that's what I can't understand, it looks as though it was installed yesterday, but it wasn't of course.

 

[Mbear]

There's only a few things left mate....

Remove flue restrictor, clean fan blades, worst case scenario is replace fan or flue