CCN1 Pipework Installation & Tightness Testing

Question 1

What does a gas tightness test confirm?

Accepted Answer

That the gas installation pipework contains no leaks — confirmed by applying a test pressure and observing for pressure drop

Answer

That the pipework is correctly sized for the appliance load

Answer

That the correct gas pressure is reaching the appliances

Answer

That all appliances are correctly commissioned

Question 2

What test pressure is used for a domestic gas installation tightness test?

Accepted Answer

Twice the operating pressure (typically around 20 mbar for natural gas) or a minimum of 20 mbar whichever is greater

Answer

10 mbar — the normal operating pressure

Answer

100 mbar to find micro-leaks

Answer

No specific pressure is prescribed — the engineer decides

Question 3

What is the standard gas tightness test procedure for a domestic installation?

Accepted Answer

Isolate appliances, apply test pressure, allow to stabilise, record pressure, wait specified time, record final pressure and compare

Answer

Simply check for smell of gas with all appliances running

Answer

Apply pressure and use a match near joints to detect leaks

Answer

Pressurise the system and listen for hissing sounds only

Question 4

What action must be taken if a tightness test reveals a pressure drop?

Accepted Answer

Trace and locate the leak(s), repair, then re-test to confirm tightness before proceeding with any gas work or restoring supply

Answer

Report to the gas transporter and await instructions

Answer

Increase the test pressure to identify the leak location

Answer

Re-test after 24 hours as pressure drops can be due to temperature change

Question 5

What material must NOT be used for gas pipework installations in the UK?

Accepted Answer

Lead — lead pipework is prohibited for gas installations due to its toxicity and poor joint integrity

Answer

Copper — it is not suitable for gas

Answer

Steel with threaded joints — only press-fit is permitted

Answer

Plastic — all plastic pipework is prohibited for gas

Question 6

What pipe sizing consideration is critical to ensure correct gas appliance operation?

Accepted Answer

The pipe must be sized to deliver the required gas flow rate (volume) without excessive pressure drop — undersized pipes starve appliances of gas

Answer

Pipe sizing only affects the time taken to purge the system

Answer

Oversized pipes always improve appliance performance

Answer

Pipe size is only relevant for commercial installations