An interesting sequel to all this:
The replacement appeared to work in that moving the sliders up and down made a noise but that was probably the boiler firing up - but not the pump.
Consequently the radiators did not come on.
While trying to work out where all the connections led to...
Also one more point.
Until this is replaced if I turn the boiler OFF I assume the faulty timeswitch won't prevent it restarting when I turn it on again ?
Thanks Mike for your advice.
Is there a replacement model you would recommend given that I would not need any more advanced features than the current device provides
After a power cut I found that my Potterton EP2000 is not working. There is no time display and moving the sliders has no effect.
The heating and water remain ON (which surprised me as I thought they would be off)
The Potterton is over 25 years old.
Before I call an electrician do you...