Hey Uug,
Thanks for the tip. Unfortunately being a Bungalow we are on solid concrete floors and guess where all our pipework is........Yep, under the concrete.
I have no idea where the pipework runs, the only visible heating pipework is that of the extension Rad that has been 't'd. How far away from the boiler should I/could I tap into the main flow and return? There is at least 4 foot of pipework in the cupboard from the boiler at head height before it dissapears into the concrete abyss but if I can only tap into the horizontal run I'm screwed. I may end up just living with the rad not working and take it away completely. No point in having cold water running around a system.
Cheers mate.