Hostmann 425 Diadem Tiara help

[electrajohnt]

could anyone help please.

Horstmann 425 Diadem Tiara.
The dial rotates automatically along with the tappets but the tappets do not change the range. I can change the range manually by operating the advance switch.
Is this a problem that I can fix or do we need a new unit.
Help please. JohnT

 

[Sharpend]

You could change it for one of these as a direct replacement. 

https://www.heatingcontrolsonline.co.uk/horstmann-h27xl-series2-channelplus-p-59.html

 

[electrajohnt]

You could change it for one of these as a direct replacement. 

https://www.heatingcontrolsonline.co.uk/horstmann-h27xl-series2-channelplus-p-59.html

Thanks' Sharpend, I will see if anyone comes up with a fix first.