Knocking in Boiler

[kevin12345]

Hello,
I decided a few days ago to turn up the Temperature a little on my 14 year old Glowworm 40FF Boiler to put a little more heat in the radiators.
I only turn up the Min Max Knob a little bit and as soon as I did I started getting a knocking/cracking of pipes sound straight away. The knocking seems to be about every 10 seconds for about the first 3 minutes of fire up until it goes but every time the boiler fires back up it starts again, even when cooling back down it knocks but not as loud.
I put the heating knob back to the original setting it was on before I changed it but it is still knocking.
Any body any idea how I can get rid of this noise?
The noise definitely seems to be coming from the boiler
I'm not going to play about with the boiler, just wondered if there was anything outside the boiler I could do to get rid of it?
Thanks

 

[ianmcd]

Why did you feel the need to turn it up in the first place ? were the rads not heating like they used to ? sounds like you may have a blocked cold feed

 

[kevin12345]

Felt a little chilly and compared the heat coming from a couple of friends radiators and decided mine were not getting quite as hot so I turned up the Boiler a little and the knocking started.
Any idea what the knocking is?

 

[BARNY78BG]

Boiler sounds like it is kettling due to sludging of boiler/system

 

[kevin12345]

Any solution's then?