Worcester Bosch Oil Boiler Problem

[Joncamp]

Hi All

We have a 2 year old Worcester Bosch Greenstar Danesmoor 18/12 External boiler with a Riello RDB burner. Last week it stopped working, would just purge, try and fire for 5 secs then go back to purge. At this point I changed the Photocell for a new Riello one - same result.
Called a local engineer who came and looked at it. He changed the photocell, tested oil pressure, cleaned burner & baffles, replaced ignitor leads but no improvement. He then changed the control box - same issue. Checked oil filters and ran off some oil - all fine.
Changed the photocell again - same result. After 4 new photocells ( I checked they were the correct ones and new) he has thrown the towel in.
If I start the boiler and then remove the photocell as soon as it fires it will run (in daylight) so clearly the cell is detecting light, just not enough when it is running.
I am now looking for another engineer, the earliest so far I can get is 5 days away.
Does anyone have any ideas? Either there is a huge batch of dud photocells or something else.
Help!

 

[BoilerBob]

Have you got the right photocell you may need a digital one as there are now
two types of cell. Bob

 

[muggles]

There are two types of photocell and two different control boxes for these now. Get the combination wrong and it won't work.

EDIT Bob best me to it