The let-by, temperature stabilisation, and tightness test sequence for domestic properties.
A tightness test assesses pressure behaviour under defined conditions. Establish the gas, pressure stages, test boundary, installation volume, connected equipment and applicable procedure before judging the reading. A smell check or stationary meter display cannot replace it.
Edition 4 and the changeover
IGEM published UP/1B Edition 4 in March 2026, expecting adoption as soon as reasonably practicable. It becomes effective on 1 October 2026; Edition 3 is withdrawn on 30 September 2026. Use the applicable published edition, including its amendments, rather than a draft or an unlabelled saved table.
Establish a valid test
The selected procedure determines the instrument, test pressure, isolation checks, stabilisation and timed interval. Gas passing a closed control can mask a loss. Warming or cooling can also move pressure: an elapsed minimum does not prove stability if the reading is still drifting. Resolve those conditions instead of inventing a correction afterwards.
Identify what is losing pressure
Under Edition 4, installation pipework must be proved tight. With existing appliances connected, an observed loss requires investigation: isolate the appliances where reasonably practicable and retest the pipework and meter. A perceptible loss from that section fails; a meter being fitted does not create a leakage allowance.
If it is not reasonably practicable to isolate the appliances, the connected test must achieve no perceptible movement. Pipework with new appliances also has no permissible loss.
Only after pipework tightness is established can an eligible existing-appliance loss be compared with the applicable fuel-gas and installation-volume limits. A smell of gas still means the result cannot be accepted. A within-limit number alone is incomplete evidence.
Complete the job
Make safe, investigate and rectify unacceptable results through the proper competent route, then retest. A result does not authorise adjustment of a sealed regulator. Before return to use, complete required purging, appliance checks and records. Purging under Edition 4 requires installation volume to be calculated and purge volume determined as PV = 1.5 × IV.
These are revision decisions, not a full set of live valve operations or a table of test pressures and times.
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