What is tightness testing?
A tightness test is the safety check every Gas Safe engineer carries out on gas pipework to confirm there are no leaks. It's done before a new boiler is connected, after any pipework is altered, and as part of a gas safety inspection. Put simply: it proves your gas installation is sound and safe to use.
In March 2026, the Institution of Gas Engineers and Managers (IGEM) released IGEM/UP/1B Edition 4 — the biggest update to tightness testing in over a decade. It replaces the long-standing Edition 3. ## The transition window: March – September 2026
Edition 4 was published in March 2026, but there's a 6-month transition period ending 30 September 2026.
- During this window, both Edition 3 and Edition 4 are valid.
- From 1 October 2026, full compliance with Edition 4 is mandatory.
The Gas Safe Register has confirmed they won't defect businesses for using the older procedure during the transition, but after October it's the only accepted method.
The big change: Installation Volume over meter size
Previously, engineers worked out the acceptable pressure drop based on the size of the gas meter (for example a U6 or G4). Edition 4 scraps this approach for natural gas.
Permissible limits are now dictated by the Installation Volume (IV) — the actual volume of gas the pipework system can hold. This brings natural gas testing in line with the stricter standards already used for LPG.
What this means in practice
If an engineer sees any "perceptible movement" on the gauge, they can no longer just check a meter-size table. They now have to calculate the specific volume of the system (or the section) being tested.
To save time on smaller systems, if the drop is below a certain threshold — for example less than 1 mbar for natural gas — the system qualifies as an automatic pass and no calculation is needed.
Pipework integrity: zero tolerance
One of the most important safety updates in Edition 4 is the new emphasis on pipework integrity.
The standard now makes sure that even a "permissible" leak can't be hidden inside the building's infrastructure. If a pressure drop is detected but still falls within the permissible limits for the whole system, the engineer must now:
- Isolate all appliances
- Repeat the test on the pipework only
For the pipework-only test, there must be no perceptible movement on the gauge. If the needle moves at all, the test is an immediate fail. The goal is to prove the pipework itself is 100% sound.
Simplified purging procedures
Purging — the process of clearing air from gas pipework before use — has also been streamlined. A single, universal calculation now applies across all installations to work out the Purge Volume (PV):
PV = 1.5 × IV
By making the calculation strictly volume-based, every purge is consistent and safer, regardless of the meter's capacity.
New permissible limit benchmarks
The new tables categorise pressure drops based on the total cubic metres (m³) of the installation. Key examples:
| Fuel type | Installation volume (IV) | Max pressure drop | | --- | --- | --- | | Natural gas | < 0.005 m³ | 8 mbar | | Natural gas |
0.015 – < 0.035 m³ | 1 mbar | | LPG | < 0.0025 m³ | 2 mbar | | LPG |
0.01 m³ | No perceptible movement |
Crucial reminder: For any system consisting of pipework only (or where only brand-new appliances are being connected), the standard remains no perceptible movement allowed.
How does this impact you as a customer?
Safer installations
The new rules mean even tighter checks on your pipework. When we install a new boiler or alter your gas pipework, you can be even more confident the installation is completely leak-free and safe.
Slightly longer on-site time
Because engineers now calculate Installation Volume and, where needed, isolate appliances and re-test pipework, some jobs may take a little longer than before. This is a small trade-off for a noticeably higher safety standard.
New builds and first-time installations
If you're having a brand-new boiler connected, the pipework must show zero movement on the gauge. Our engineers are already fully trained on the new procedure, so your installation will be carried out to the latest standard.
Landlord gas safety checks
If you're a landlord, your annual CP12 gas safety inspection will now be carried out to the Edition 4 procedure. The good news is this gives you an even stronger guarantee that your rental property meets the very latest safety standards — which is valuable protection for you and your tenants.
How Sanju's Heating is prepared
Our Gas Safe registered engineers have already been trained on IGEM/UP/1B Edition 4 and we're fully compliant ahead of the October 2026 deadline. Whether you need a new boiler installation, a gas safety certificate, or pipework alterations, every tightness test we carry out follows the new volume-based procedure.
Book your installation or safety check
To book a boiler installation, annual service or gas safety certificate carried out to the latest IGEM/UP/1B Edition 4 standard, get a fixed-price quote or call us on 01635 74 50 40.
