Now you see it doesn't matter how confident you THINK you are it's all down to how competent you are.
In this case you are not.
Just as a learning point for you, the boiler thermostat is not in fact a "safety" device, it is a control device. The high limit stat is the "safety" device.
Hence...
Here we go, it's not rocket science but on an Internet forum asking advice.
Don't have a problem with educated people, but people need to know there limits and ultimately accept them.