My Potterton Suprema 50L boiler if turned off and then on again fires up, it remains lit for a couple of minutes then when the demand for lighting again happens a noise is heard but the boiler will not light, the Yellow LED continuously flashes.
The pcb installed is of the latest version 5111603.

Tony Smith, July 2010

external controls, ie programmer, pump, but i would guess at 3 port diverter

lee, September 2010