Dear All,

Our central heating controller is on the blink.

How straightforward is it to replace this myself?

The programmer is a Honeywell unit, no model number shown, and I don't
know how old it is. The front section hinges up and separates from a
smaller piece screwed to the wall to allow access to batteries and a
reset button.

The wall section has terminals labelled T3, T4, T7, T8 which the front
snaps onto. The unit is roughly 8 by 13 cm.

My questions a

If I buy a new Honeywell unit like the one here
http://www.plumbworld.co.uk/760-2963 - which looks a similar size to
what I have but is clearly a different design - then will it:

(a) Simply snap on the the existing wallmounted section (this would be
great)

(b) Require the same four wires as I have in the wall now, but require
me to connect them anew to the new unit (this would be fine)

(c) Require different wires from what I have now (this would be a
nightmare!)

Any and all advice gratefully received!