IGEM/UP/1B Edition 4: what changes on 1 October 2026
By Jordan Valentine-Dunn, Gas Safe registered engineer · 28 September 2026
From 1 October 2026 every tightness test on a small natural gas, LPG or LPG/Air installation follows IGEM/UP/1B Edition 4, and Edition 3 is withdrawn on 30 September. The permissible drop now comes from the installation volume and the fuel gas, not the meter size, and movement within limits must be proved not to be the pipework.
When does Edition 4 become mandatory?
On 1 October 2026, in all circumstances, according to IGEM. For six months both editions ran side by side, and Gas Safe Register agreed not to defect a business at inspection for not yet being conversant with Edition 4. That period ends on 30 September.
| Date | What happened |
|---|---|
| March 2026 | IGEM publishes IGEM/UP/1B Edition 4 (Communication 1903) |
| 25 March 2026 | Gas Safe Register publishes the first ISU 133 |
| 15 April 2026 | ISU 133 Edition 2 issued, superseding the first after industry feedback |
| 30 September 2026 | Edition 3 withdrawn; the six months of running both editions ends |
| 1 October 2026 | Every tightness test in scope must follow Edition 4 |
What pressure drop is allowed under Edition 4?
It depends on the fuel gas and the installation volume (IV), and applies only with existing appliances connected and no smell of gas. With pipework only, or only new appliances, no perceptible movement is allowed.
| Fuel gas and table | Installation volume (IV) | Maximum permissible drop |
|---|---|---|
| Natural gas (table 3) | Up to 0.005 m³ | 8 mbar |
| Natural gas (table 3) | Over 0.005 up to 0.010 m³ | 4 mbar |
| Natural gas (table 3) | Over 0.010 up to 0.015 m³ | 2.5 mbar |
| Natural gas (table 3) | Over 0.015 up to 0.035 m³ | 1 mbar |
| LPG/Air (table 2) | Up to 0.025 m³ | 1.5 mbar |
| LPG/Air (table 2) | Over 0.025 up to 0.035 m³ | 0.5 mbar |
| LPG (table 5) | Up to 0.0025 m³ | 2 mbar |
| LPG (table 5) | Over 0.0025 up to 0.005 m³ | 1 mbar |
| LPG (table 5) | Over 0.005 up to 0.01 m³ | 0.5 mbar |
| LPG (table 5) | Over 0.01 up to 0.035 m³ | No perceptible movement |
IGEM's FAQ explains why a small installation may lose 8 mbar and a larger one only 1 mbar: every limit is based on a leakage rate of 19 ml per minute for the installation volume, so the two are roughly the same escape. The Registered Gas Engineer article says the LPG table is unchanged from previous versions.
What else changes in the procedure?
| Rule | Edition 4, from 1 October 2026 | Compared with Edition 3 |
|---|---|---|
| Permissible drop | Read from the IV and the fuel gas | Changed: it was based on the meter size alone |
| Movement within limits | Isolate the appliances and retest the pipework and meter; no perceptible movement allowed | New: confirming the drop was not on the pipework was not previously required |
| Purge volume | PV = 1.5 x IV on every installation, so the IV is worked out whenever you purge | Changed: a PV of 0.01 m³ could be assumed for pipe up to 28 mm and a meter up to 6 m³/h |
| Low test pressure | If the test pressure cannot be reached, isolate and investigate; natural gas may be tested at 18 mbar minimum, with IGEM/G/13 operating pressure checks after a pass | New note in Edition 4 |
| No perceptible movement | 0.25 mbar or less on a fluid gauge or an electronic gauge; 0.2 mbar on an electronic gauge reading to one decimal place | Stated in ISU 133; the published summaries do not say whether it changed |
| Smell of gas | A fail whatever the gauge shows | Not listed as a change; IGEM's FAQ states it |
| Record keeping | Gas Safe Register recommends recording which edition the test followed | New recommendation |
How does a test work out in practice?
Two natural gas examples with existing appliances connected, after the let-by at 7 to 10 mbar for 1 minute, 1 minute to stabilise and the 2 minute test at 20 mbar. First, the water gauge drops 0.8 mbar. That is perceptible, but it is below 1 mbar, the smallest natural gas limit, so IGEM's FAQ says it is within limits without working out the IV. You still isolate the appliances and retest: any perceptible movement on the pipework is a fail.
Second, the gauge drops 3 mbar on an installation whose IV you work out at 0.012 m³. That band allows 2.5 mbar, so the test fails: trace and repair the escape or make the installation safe under IGEM/G/11. After the repair, the purge volume is 1.5 x 0.012 = 0.018 m³, which is under 0.02 m³, so natural gas may purge to air. LPG and LPG/Air always purge to ignition.
How is the installation volume worked out?
By adding the internal volume of the pipework, its fittings and the meter, from Appendix 7 of the standard, which IGEM sells rather than publishes. IGEM's scope examples show the size of 0.035 m³: 25 m of 35 mm copper with a U6 meter, or 10 m with a U16, both come in under it. Where pipe disappears into a wall, the Registered Gas Engineer article says to assume the largest visible size, so the IV is overestimated, never under.
Work it out
Does Edition 4 cover every installation?
No. IGEM's scope is installation pipework with a nominal bore up to 35 mm, a meter badged up to 16 m³/h, an IV up to 0.035 m³, a maximum operating pressure at the emergency control valve up to 2 bar for natural gas and LPG/Air, and an operating pressure up to 21 mbar for natural gas and LPG/Air or 37 mbar for LPG. Above 0.035 m³, IGE/UP/1 applies. LPG service pipework is outside it.
This summarises published guidance, not the whole standard, which ISU 133 says engineers must know. Only a Gas Safe registered engineer may carry out a tightness test, or install, service or certify a gas appliance. If you smell gas, call the National Gas Emergency Service on 0800 111 999.
When you record the result, Manifold's check page carries the same Edition 4 calculator and saves the edition, fuel gas, IV, drop and result against the job, printed on the Landlord Gas Safety Record.
Frequently asked
Sources
- Gas Safe Register, Industry Standard Update 133 (Edition 2), 15 April 2026
- Registered Gas Engineer, Updated tightness testing standard: what you need to know, 11 May 2026
- IGEM, IGEM/UP/1B Edition 4: scope, publication and effective dates
- IGEM, Frequently asked questions on IGEM/UP/1B Edition 4
- National Gas, emergency contacts