Problem with central heating timer

Hoping you guys can shed some light on this - I'm not techinically minded so go easy!

Our basement is on a separate timer system (a Hortsman 425 Tiara). It's was probably 10 years old and the clock dial stopped working.

I bought an exact replacement, on the basis that it would be easier to install and avoid any rewiring. The replacement works fine on 24hrs and all day, but the clock dial does not rotate at all if it is set on twice or off.

The old one may in fact have had the same problem, I can't recall whether I tested the different settings and I damaged it when taking it off (I didn't have the instructions )

The baseplate seems to be all wired correctly. Any idea what could be causing it not to work in certain modes?

Thanks.

If it is working in 24hr/all day and going round then it's unlikely to be anything else but a faulty clock.

Thanks, that seems to make sense.

Now I am confused. Got a replacement and encountering the same problem.

Is the HCL9 backplate an industry standard, as may try to get a different make of programmer and am not up for any rewiring.

Thanks.