Thank you both for your replies. Regarding the bypass screw, these are supplied separate and only need to be fitted when using a two pipe system. It wasn’t the pump at fault as advised by a Oftec registered engineer or the photo cell in the end but a mixture of unburnt fuel and soot blocking up...
I found that my oil pump on my RDB1 burner was leaking from a none servicable part
(Drive shaft)
I bought a new pump and fitted it and then got an engineer out to set it up.
He couldn’t set the pressure because as soon as the burner fires up the pressure keeps on rising and doesn’t respond to...