Just had a company install a new heating system into my home. the copper pipes are fitted perfectly but there is a huge banging noise which happens on and off and is audible when the house is quiet. The noise seems to ring around the house but not in any particular order. The noise is extremely loud and on occassions EXTREMELY LOUDDD. The system as been bleed. The noise is also there even when the heating is off. I have 5bar pressure coming into the house. ANY thoughts! 
