Thank you John and Roger for the quick answer.

On Mon, 22 Oct 2007, Roger Mills wrote:

In an earlier contribution to this discussion,
Kostas Kavoussanakis wrote:

I would like to replace my old (80s) Honeywell room thermostat with
the 907. It's a very common model.

snip

Am I right that this a DIY job? I know I need to switch the boiler
off at the mains and drop the fuse while the wife and kids are out
shopping :-)

Your last question worries me! It's a simple job - well within the scope of
a *competent* DIY-er - but the fact that you had to ask, and couldn't work
it out from the Honeywell literature - not to mention being uncertain as how
to isolate it when working on it - makes me wonder whether maybe you should
be getting some professional help.

Thanks for your concern; what's uncertain about dropping the fuse? :-)
Sure, I will check for current at the terminals as well, isn't that
standard?

The reason why I felt compelled to ask if it's DIY was the quote I got
from my gasman for this replacement: 70 pounds. Also, the standard set
of questions from Honeywell mentions a sub-base as a possibility; I am
not sure how that is defined, so I thought this could be an issue. In
general I thought I had underestimated its complexity.

Also, it's a moot point whether it's notifiable under the dreaded Part P -
since central heating controls seem to come within its scope. I'm not sure
how convincingly you could argue that it's a 'like for like' replacement.

That's important to me: who does one ask? My case would be that it's
"like for like" in the sense that the new thermostat performs the same
electrical task; it just does it in a internally different way.

Thanks!

Kostas