It is good practice when filling a system for the first time to

• A. Fill distribution pipework first
• B. Fill hot water pipes first
• C. Fill cold water supply to cistern
• D. Open all taps at once

Answer: (A)

Priming and purging the system is the aim when you fill it for the first time. Filling the distribution pipework first ensures the main network becomes full of water and air is driven out through outlets as you go. This sets up a continuous water column throughout all branch lines before any storage vessel feeds the network, so there aren’t air pockets left that could cause sluggish flow or air locks in upper parts of the system. Once the distribution is primed, filling the cold-water storage cistern won’t push air into an empty or partly filled network and will maintain steady pressure across fixtures. Filling hot water pipes first isn’t necessary for a cold-water system and isn’t how you reliably purge air; filling the cistern first can trap air in the distribution lines, and opening all taps at once isn’t a proper filling method and can cause pressure shocks.