Boiler banging and making streaming noise

tm0019

I’ve just been woken up by my boiler banging really quite loudly.

It seems to be making a streaming noise, as though waters running through it constantly, but I don’t see any water around the area. The pressure is high and when I lower it the noise dies down but as soon as I turn the switch back the pressure instantly rises and is back to making the streaming noise.

I’ve switched it off at the wall and had to turn the water off (to stop the streaming noise). 

Does anybody have any idea of what it could be? 

JohnNY

I'm guessing you've got a runaway pressure condition which is usually caused by a clogged pigtail: the curled pipe on the side of the boiler on which the "pressuretrol" (pressure regulating device) is mounted.
Posting pics pf your boiler here is always very helpful.