Overheating.. near boiling water issue

Hi All,

Hope all is well, Im having a issue with my pulsacoil 3 and hopefully you could shed some light on this..
For a while now I have had to keep resetting the reset switch on the system but a few days ago the water coming out was sooo hot it nearly burnt me..

Could this be the heat sensor? or the rod thermostat? if so are these easy to replace? or do you think it could be something else..

Ah also, the top up cistern now needs to be topped up every other week, I cant seem to find any leaks anywhere so im not sure why this would be..

Really appreciate your help and many thanks in advance

Sounds like rod stat.
So if boiling would lose water?
Check the stat by removing and using hot water from a kettle.
And temperature probe etc.
Mike