As a follow up to this, the switch in this part was fine but it had become loose in the housing causing the switch to not fully engage. As a stop gap while I was waiting for the new part, I was able to wedge the switch in position fixing the heating issue.
Can I ask, how is the safety pressure switch (part 474) removed? Does it screw off? I have been into the bottom but it seems fixed solid and I don't want to break anything by forcing it if it is removed in a different way.