can you run some underfloor heating from a combi boiler for an extension on my house? is this a good idea, is it worth doing? many thanks

Yes you can do this. I'm no plumber but had this done on my house and it works very well. I had a kitchen extension which went in after the boiler and is the only room in the house that has underfloor heating. Someone might be able to give you a bit more info.

Yes this is not a problem to do, u'll have to zone your house so the heating works independantly from the underfloor,

i am thinking about doing this, i have seen complete kits by speedfit in the screwfix catalogue, is this the best way to install only one circuit in a new room? i know some people cobble togther their own controls and circuits...

i've not seen the screwfix package, but if your attaching off a combi u'll need a 2 channel programer, 2x 2port valves, manifold and pipe, not sure if you can link seperate room stat as not electrician but if you link it to one of the valves think quite possible. have fun