, my name is ***** ***** I have been in the home improvement and repair field years. I will be very glad to help you today. Is there water coming out of the temperature relief valve? Also have you checked the expansion vessel? If you release air out of the air valve on the pressure vessel and water comes out then you need a new vessel. If no air comes out then it needs to be pressured. If it does need to be pressured then pressure it and release some air again and see if water comes out. If water comes out then the diaphragm is broken inside.
potterton profile boiler doesn,t have expansion vessel,