Firebird overheat stat fault?

[LesCM19]

When I was bleeding radiators, steam was coming out, not air. Switched boiler off when pressure went over 2.5 as I'd never seen it that high before, usually 2 when up to temp. Pressure Control stat was clicking when knob was turned on warm up but when hot it didn't seem to be doing anything. I know expansion tank needs replacing which I can do myself but what can be going on with the various stats & cutouts? Thinking of getting someone in for that

 

[Exedon]

First needs expansion vessel sorting .
Could easily be lack of circulation causing overheating.
As you seem to be heading that way get a competent oil engineer out rather than throwing parts at it.