On Fri, 12 Dec 2008 04:20:06 -0800 (PST), wrote:

To heat the kitchen properly we need to have the boiler on quite high
which makes the other rooms too hot. I tell my missus we should keep the
boiler on high and turn the thermostatic valves down in the other rooms
but she thinks this will use a lot more energy than turning the boiler
down and having the thermostatic valves fully open in the other rooms
and put up with the chill in the kitchen. How can I explain to her that
she is wrong?

With difficulty and I don't think, unlike other posters, she is correct.
They seem to have missed the fact the rest of the house is too hot. Thus
lots of energy is being used there that could be used to heat the kitchen.
Basically it's not possible to say if the fuel bill will go up or down.
I'd be tempted to go on the down slightly side as the rest of the house
will lose much more heat than just the poorly insulated kitchen.

What you need to do is set the TRV's in each room to the temperature you
find comfortable but comfort is very much based on what you are used to.
Suddenly lowering the temperature of rooms may well generate complaints.
Some people find a room at 22C comfortably cool, I'd be roasting in it.
Make small adjustments over a few weeks.

--
Cheers
Dave.