Setting - PMA KS50 Industrial Temperature Controller

New to the forum on the hope someone can help.
We are very small company with limited expertise for some components of our machines.

We have an old KS 50 controller that controls the temperature on a plastic sheet Preheater which feeds a thermoforming machine. We have always had issues with it since day one.

The heater runs OK for a period of time at a stable 110c but after a few hours if left idle goes up to 130c and sometimes switches off. We have had the preheater unit checked over 4 times by an electrician and replaced all the parts that we think it could be the issue to no avail.

Our last point of call is the controller. We have the manual but to be honest its so complicated and reluctant to just start changing figures without knowing what we are changing.

Can anyone give us guidance or put us in contact with a company who could help? We really do not want to replace the existing control just set it up correctly for our application.

Any assistance would be much appreciated.

(we are based in the southwest of the UK)