potterton flowsure plus?

hot water and central heating work however my problem is this:
couple of weeks ago boiler seemed to 'cycle' and keep firing up regularly, and getting hotter than normal. one day it overheated whilst taking a shower. sounded like air in system so i bled boiler- some air came out but also very hot water /steam also. temp gauge around 90, pressure around 1.5 bar. have turned dhw now to minimum water temp but still temp can rise to 90 on gauge. hot water from taps very very hot. any ideas please??