Banging and pressure loss at taps / shower

[paradoxni]

We have a gas fired central/water heating system.

When we require hot water (taps or shower) the boiler fires up and heats the water when tap opened and will then run fine for several minutes.

Then there will be a knocking/banging from the boiler (in the kitchen), the pressure reading will jump up and down and the water from the tap/shower will slow, stutter and finally stop completely.. the flame will then go out on the boiler and the heating will cut out for a few secs. The gas then ignites again, the hot water begins to flow from the tap/shower normally for another few minutes until the whole problem repeats.

Pressure was about 0.75 bar and today I increased this using the top-up to 1bar to see if the problem would be fixed, but unfortunately not.

Im no expert but it "sounds" like there is air trapped in the system.

We also have an electric shower in the ensuite and the water stopping completely seems to have caused this to blow. - Althou perhaps this is a seperate issue if the electric shower is only connected to the coldwater.

Is there a simple solution to this or should I just bite the bullet and call out a heating engineer?

 

[paradoxni]

Sorry forgot to add.. I discovered some drops of water coming from one of the pipes below the boiler, around one of the large nuts. The amount that drips out is very small and barely covers the bottom of the small bowl i have placed underneath - its evaporates quicker than it leaks.

Is this related to the problem above and would it be as simple as tightening the nut in question.