Tightness testing changes on 1 October: IGEM/UP/1B Edition 4 explained

If a test fails: what to do on site

First, trace and repair the escape and test again — if you can put it right there and then, with the customer's agreement, that's the aim. If you can't, work down this list:

1. Tell them. Explain that it's Immediately Dangerous, why, and that it mustn't be used until it's put right — using it would break the Gas Safety (Installation and Use) Regulations.
2. Disconnect and cap it, with the customer's permission, using an appropriate fitting. With nobody in, disconnecting is still recommended (in non-domestic premises, check who can make that call first).
3. If they refuse: turn it off if you can, then call the gas emergency service on 0800 111 999 (for LPG, the supplier's emergency line). Get a job reference number and the time of the call, explain what you've done, and stay nearby if you reasonably can to talk the attending engineer through it.
4. Label it. Attach a DANGER DO NOT USE label where it will be seen. If the appliance is in a cupboard, put a second label on the door.
5. Fill in a warning notice headed DANGER DO NOT USE: the fault, what you did, and what needs doing. Get it signed — if they won't sign, write that down. Give them a copy and keep one. With nobody in, leave a copy on site.
6. Tell the owner in writing if the person you're dealing with doesn't own the property — a tenant's landlord or managing agent needs the details too.
7. Check whether it's reportable. Under RIDDOR 11(2), report it to HSE online within 14 days if it's down to bad design, installation or servicing and was dangerous enough to have caused, or be likely to cause, death, unconsciousness or a hospital visit — even if you've already fixed it. Other poor workmanship can be reported to Gas Safe Register.

A let-by isn't the same thing

If the pressure rises during the let-by test, the emergency control valve is passing gas and the tightness test can't be relied on. A letting-by ECV with no smell of gas is At Risk, not Immediately Dangerous: notify the gas emergency service, or the gas supplier for LPG.

What changes, and when

IGEM published Edition 4 of IGEM/UP/1B — the standard for tightness testing and direct purging of small natural gas, LPG and LPG/air installations — in March 2026. Gas Safe Register set out the key changes in Industry Standard Update 133, reissued as Edition 2 on 15 April 2026 after engineers found the first version confusing.

Edition 3 and Edition 4 have run side by side since then. Edition 3 is withdrawn on 30 September 2026, so from 1 October Edition 4 is the only one you can work to. Gas Safe said it wouldn't record a defect against a business for not yet being fully up to speed during the changeover — that grace ends with the transition.

The test itself is broadly the same. What's changed is how you read the result, and what you do next.

What Edition 4 covers

IGEM/UP/1B applies to small installations — all of these:

• an installation volume of 0.035 m³ or less supplying a single dwelling or non-domestic premises
• pipework no bigger than 35 mm nominal bore (DN32, R1¼)
• a meter, if there is one, with a badged capacity of 16 m³/h or less
• a maximum operating pressure at the ECV outlet of 2 bar or less for natural gas and LPG/air

Edition 4 explicitly includes installations on caravans and leisure accommodation vehicles (LAVs), as long as they sit within those limits.

It doesn't cover boats, yachts and similar craft — small LPG installations on those are tested to PD 54823 or BS EN ISO 10239 — or LPG service pipework, which is covered by Liquid Gas UK Code of Practice 22. Anything over 0.035 m³ is tested to IGEM/UP/1 or IGEM/UP/1A.

The test, step by step

1. Prepare. Visual inspection first. Make sure appliances are set up for the test — cooker lids up, permanent pilots out.
2. Let-by test. Turn off the ECV (or the appropriate valve), connect the gauge, and test at 7–10 mbar for 1 minute. There must be no rise.
3. Tightness test. Raise to the tightness test pressure for the fuel gas, let it stabilise for 1 minute, adjust, then test for 2 minutes.
4. Read the gauge. No perceptible movement means the installation is gas tight — you're done. Pipework on its own, or a system with only new appliances, must show no perceptible movement at all.
5. If it moved, with existing appliances connected: work out the installation volume and compare the drop with the allowed figure for that volume and fuel gas (below). Over the limit is a fail.
6. Inside the limit? Retest the pipework on its own. Isolate every appliance and repeat the test on the pipework only. It must show no perceptible movement. If an appliance genuinely can't be isolated, test with it connected and apply the no-perceptible-movement rule instead.
7. Finish. Remove the gauge, refit the test nipple and restore the gas. Check every disturbed joint with leak detection fluid, including the pipework between each isolation valve and the appliance it serves. There must be no smell of gas.

Allowed drops by installation volume

These are the maximum drops over the 2-minute test for installations with existing appliances connected, as published in ISU 133. They only apply where no smell of gas has been reported. Installation volume (IV) is in m³.

Natural gas

LPG

LPG/air

Above 0.035 m³ the installation is outside IGEM/UP/1B altogether — test it to IGEM/UP/1 or IGEM/UP/1A.

What “no perceptible movement” means

On a fluid (water) gauge, a movement of 0.25 mbar or less counts as not perceptible — so if you can see it move, it's moved more than that. On an electronic gauge the limit is 0.25 mbar, or 0.2 mbar on a gauge that reads to one decimal place.

Working out the installation volume

The installation volume is the pipework plus the meter plus fittings. You don't need it when the gauge doesn't move — only when it does, to know which limit applies. The commonly used figures:

The pipe figures include 10% for fittings. Worked example: a U6 meter with 10 m of 22 mm and 5 m of 15 mm copper is 0.008 + 0.00352 + 0.00077 = 0.0123 m³. On natural gas that falls in the 0.010–0.015 band, so the allowed drop is 2.5 mbar — not the 4 mbar a U6 meant under Edition 3.

Purge volume

The purging procedure itself hasn't changed, but working out how much to purge has. Instead of reading it off the meter size and pipe diameter, it's now 1.5 × the installation volume on every installation. For the example above, 1.5 × 0.0123 = 0.0185 m³.

Common questions

Do I need to redo certificates from before 1 October?

No. A test done properly to Edition 3 during the transition was valid. Edition 4 applies to tests from 1 October onwards.

Is the Unsafe Situations Procedure changing too?

No — that's a different document. The current version is IGEM/G/11 Edition 2 with amendments to July 2025. Only the tightness testing standard, IGEM/UP/1B, moves to Edition 4.

Does this apply to commercial jobs?

Only small ones — see what Edition 4 covers. Most commercial installations are bigger than 0.035 m³ and are tested to IGEM/UP/1 or IGEM/UP/1A.

Do caravans need anything different?

They're now covered by the same standard, so the same procedure and the same limits apply, provided the installation is within scope. Boats aren't — they have their own standards.

Why the pipework-only retest?

The allowed drops exist because existing appliances can account for a small, harmless loss. The retest proves the drop isn't coming from the pipework — which is where a real escape would be.

How does OnPoint handle it?

Every OnPoint gas record with a tightness question — the landlord and homeowner gas safety record, service record, inspection record and more — has a Help me do the test box that walks the Edition 4 procedure, works out the allowed drop from your pipe lengths and fills in Pass or Fail. The tightness testing certificate records the full readings, and there's an Unsafe Situations checklist for when it fails.

Sources

This is a plain-English summary to help on site. The standard is the authority — make sure you're familiar with the full published text.

• Gas Safe Register, Industry Standard Update 133 (Edition 2), 15 April 2026 — summary on Registered Gas Engineer
• IGEM/UP/1B Edition 4, Communication 1903 — IGEM
• IGEM/G/11 Edition 2 with amendments July 2022, June 2024 and July 2025 — IGEM