Ah, Jerry, the very person I need to speak to. The B F pump pumps, nice flow from by pass, close by pass, nowt going in to boiler. A large syringe on the inlet produces the same result, all clear, nice flow, as soon as bypass closed, nothing going into boiler. I opened up the boiler check valve when it had cooled off, the little ball dances up and down when I inject water into inlet with syringe. I am going to take check valve off the boiler tomorrow and have a proper look to see if there is a blockage. With having the preheat coil in the condenser/oil trap it fills up very quickly and water starts passing up the exhaust in the chimney, so I may have to rethink that one as well. What pressure is your boiler running at? Mine is set at 45psi.
Nick.