Thanks for help but problem has been found.
The fan stops after a couple of minutes even when connected directly to the mains.
The system was correctly detecting a pressure failure and shutting down.
I have Glow Worm FuelSaver 35F.
It ignites OK but after a couple of minutes it switches of (the over heat cut off does not trip). When left for ten minutes the boiler re-ignites and the process is repeated.
Any ideas how to resolve the problem would be much appreciated.
The pump, fan, valve...