Not sure about the standard for oil boilers but all new gas boilers should have a mag filter added as part of the install. Did the installer not discuss that with you? Might be worth a quick chat with him.The boiler (new Grant Pro 15/26) does not have room and I have no idea where the last return pipe from the rads is.
Oh and please start a new thread as per site advise - resurrecting old threads can make things really confusing.