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)

When starting to fill a system for the first time, charging the distribution pipework first is best because it gets the main network of pipes wetted and pressurized early. This allows air to be pushed out through the highest outlets as you progressively open taps, so you can purge air from the system and spot any leaks sooner. If you try to fill hot-water pipes or a cistern branch before the main distribution, air can get trapped in sections of the cold line or at fixtures, making the system harder to bleed and potentially causing uneven flow once in service. Opening all taps at once is overly disruptive and can cause a sudden surge or water hammer, wasting water and putting stress on fittings. So, priming the distribution pipework first ensures a clean, air-free start and smoother subsequent filling of hot and cold branches.