Hi all,I am looking for some advice,I am doing a bathroom refurbish for my daughter,I have to change the existing radiator for a newer type,my problem is as the lives in a ground floor flat,I do not have access to any loft header tank.I am surmising it is a gravity fed system,it is not a combi system,and the boiler is old.would I be correct in turning off all radiator valves ,that way any water loss is only what's in pipe from bathroom to next radiator,is this feasable ? also as I am fitting new chrome valves could i use 15mm chrome pipe with the reducers below floor surface?the pipework is microphone,any answers would be appreciated,cheers