Old Firebird 90 thermostat issue?

[unhandymann]

Sorry wrong diagram attached there (that's the 1 channel version)

This is the correct new Diagram (R) and old (L)

 

[Avo Mk8]

i was just about to post saying that was single channel programmer!!
I can't tell how you've wired it from the pic though!
They do seem to have equivalent terminal numbers, so if you just transferred the wires over it should be equivalent.

 

[Avo Mk8]

Try disconnecting the "central heating off" wire from terminal 2 and insulate it (eg Wago connector or choc block or similar) and tuck it out of the way. Just temporarily.
See if it makes any difference.

There's something weird about the wiring of your setup.
The "off" connections on a programmer are normally only used for Y plan systems.
Yours is an S plan, so I wouldn't expect either "CH off" or "HW off" terminals to be used.
In my experience the "CH off" terminal is never used in either of the above traditional schemes, so I don't know why you have a wire on it in the first place (or have any idea where it might go!)