How to test per 2007 grant temperature controller

[RayPlumb]

I have a client with grant vortex combi 21 condensing 2007. Looks similar to be new vortex 21e but the control panel is different. Has a few seperate circuit boards and clear relays.
The fault is that it just stays on when central heating on until high limit kicks in. I've checked for trapped air (auto air vents) ok.
The hot water when used runs a bit then boiler switches off when stored hot water is hot as it should.
I want to test the temperature stat as when turned you can not hear any click at temperature change when rotating. This control knob seems to go through to a circuit board. (looks like MPCBS54 ) . Question is how do I test this to see this Stat is working OK..?

 

[SimonG]

The stat is goosed, needs a new board.

Not the greatest of designs that one.

 

[RayPlumb]

Took a bit of working out but looked like someone had switched the thermistors sensors for hot water and heating in the wrong phails holders, The thermostat seems to be working. Hot water pump runs a while (and rattling )before stopping. Could the rattling cause cavitation and air getting trapped at the top at the non venting Auto air vents... Fingers crossed