I normally now and again have to feed some pressure to get the hot water correctly.
So the other day I had gone to do the same and the nose came off and the pressure went full. I tried my best to close the valve but I was too slow. Now when I turn the boiler on it fires up and then suddenly make a loud cracking noise like the boiler is about to fall apart and the fire goes but the noise continues.
Pressure is zero when boiler fires up it goes to maximum 0.5 and the switches of.

Someone please help me

HELP!!!, February 2012

If you have to top up pressure now and again, YOU have a leak. Boiler pressure is normaly at 1 bar COLD.
So go on that, Get the leaks fixed. Then come back here if needed.

SD, February 2012