The Salus RT500 Digital Programmable Room Thermostat is fantastic. It's easy to install, just 2 wires (plus earth but not essential)live and switched supply. With 5/2 or 7day choice (just change jumper settings, no problem) and with 5 program temperature settings per day it really does give great control over the system at a really affordable price. I have underfloor heating downstairs and rads upstairs and we can feel the difference already in a couple of days, and the response is much faster than the mechanical type with very little lag or delay in response to temperature change. So, replace the old mechanical timer with one of these, I am sure you will be as delighted as we are !