I have the misfortune to be required to fit an auto bypass valve on my son's Stelrad Ideal W central heating system and I don't know which is the flow outlet and which the return. It is heavily boxed in. Is anyone out there familiar with these antiques and able to help? I had a brain when I was younger and would have run it before dismantling the rads but now I'm not so bright. Ideally it should be scrapped but the house cost so much there's no money for anything else for a while. The thing is built in tight and I don't want to take the cover off (which I have no manual for) in case I find something I don't like. This is going by the rads which have had green sealing gunge applied to the OUTSIDE of the valves by the handful.