Christian McArdle wrote:
discover I need TRV on ALL the rads rather tham all but one, and
a room stat into the bargain.

You are mistaken.

I'm not, well, I wasn't, it was the brother in law who said /all/ rads need TRVs
and the interweb said all but one. I was firmly with the web on that one but
he disagreed. I thought that having two stats would confuse the boiler.

I /must/ have a room stat so the front room will be the rad without the TRV,
the only issue now is the cable run through the kitchen and behind the
skirting. if it is low voltage I shouldn't have a problem with parts P & L

is that right ? I'm only using a cheap £5.99 bimetallic room stat.