Begin with the properties you own or manage and establish how heat is provided. Work out what the system serves, who receives heat, who owns or controls the network, who supplies it, who bills, who maintains it and who holds the information.
Ofgem asks who operates the network and who receives heat. HNTAS asks what the network is and how it is performing. The same portfolio needs to be understood network by network.
Start with the information you already hold. Where the position cannot be established from what exists, the gap is made visible rather than glossed over. Qualified partners carry out physical inspection, engineering assessment or specialist regulatory input where needed.