Click to expand.Contact Boulter Buderus for a copy of the manual. There are two pipes because as you rightly say one is a flow (suction) and one is a return. Depending on the height of the oil pump relative to the bottom of the fuel tank you may 'need' this arrangement so you can either run a second (return) pipe back to the tank and fit a non return valve in the suction pipe or you could employ a Tiger Loop device. Both options will be shown in the manual.
If the bottom of the tank is above the oil pump to guarantee a flooded suction then you can alter the pump to bypass internally (usually by removing a screwed plug) and use only one oil pipe. Don't forget to use a currently type approved oil firestop valve (such as a Teddington KBB) and of course you will be bringing ALL the peripherals up to current standard AND having it checked by Building Control won't you?
Hope someone can advise. 1) Boiler make / model (gas or oil) Oil fired Boulter Camray 3 2) What is / is not happening Upon applying.