Potterton Combi 80 hissing steam at startup

Moved into a new house and am now the first time owner of a combi boiler. This thing doesnt seem very well. At startup on timed CH, it ignites for about 2 to 3 mins then shuts off for about 1 min. It then ignites again and make a lot of rumbling and hissing noises for about 5 mins before settling down to work normally. It can best be likened to a car cooling system that has a faulty thermostat.
Hot water drawoff when CH is on is great, but when CH is not on, it takes several mins to get any hot water out. I guess the boiler is about 5 years old
Also I occassionally get all sorts of weird noises coming out of it when a cold tap is turned on, and it shuts itself down and puts the red override light on.
Have checked the pressure meter which shows a constant 1.5
Should I be calling the boiler man in.
Tks RonJ

I would guess that the boiler is over heating at the start and this means the water is not flowing at start up, there are a few reasons for this, it could be that your pump is on the way out or you have poor water flow due to scaling, I would get it checked out ASAP

I have looked at a boiler with problems similar and the problem was the pump ? not to expensive