Thanks Andyjrb.
The noise is coming directly out of the boiler....not the pipes. We also had a new radiator fitted with a thermo valve.
Sounds like that may have something to do with it.
We have just had installed a Ferolli 25 OV boiler to replace out old condensing boiler. However it has developed a fault that the installer cant seem to fix!
a) Intermittently (every other day ish) it will run for about an hour and then start to Bang....and I mean Bang...sounds like loud...