Guide · updated 2026-09-16
Gas tightness test: what changes in IGEM/UP/1B Edition 4
Edition 4 is mandatory from 1 October 2026, and Edition 3 is withdrawn on 30 September. The change that matters on site is how you arrive at the permissible drop.
Work it out now in the Edition 4 tightness test calculator, free and with no sign-up.
The change in one line
The permissible pressure drop is now set by the installation volume, not by the meter size.
Under Edition 3 you looked at what meter you were stood in front of. Under Edition 4 you work out the volume of the installation you are testing, and the allowed drop follows from that. Two properties with the same U6 meter can now have different permitted drops, because one has 30 metres of 22mm and the other has 8 metres of 15mm.
What that means in practice
You need the installation volume before you know what you are allowed. That is the meter volume plus the volume of the pipework in the section under test, and the standard applies a fittings allowance where you do not know the actual component volumes.
So the job gains a step. Measure or reasonably estimate the pipe runs by diameter, add the meter, total it, and only then do you know what the gauge is allowed to do.
A drop inside the limit is not the end of it
This is the part worth reading twice. Where there is a drop, even one inside the permitted figure, it has to be proved not to be in the pipework. Isolate every appliance and retest. At that point there should be no perceptible movement on the gauge.
A small allowable drop is there to account for appliances, not to give pipework a pass.
Scope
UP/1B covers domestic-sized installations. Above the installation volume the standard sets as its ceiling you are into IGEM/UP/1A instead, which is a different procedure. Knowing the volume tells you which standard you are working to, which is another reason the volume calculation comes first.
Where to get the figures
The permitted drops, the volume tables and the test durations sit in the standard itself, and IGEM's standards are copyright. We are not going to reproduce the tables here. Gas Safe Register published the detail in Industry Standard Update 133, and IGEM published its own UP/1B FAQ, and if you are testing to Edition 4 you should be working from your own copy.
If you have not read Edition 4 yet, do that before 1 October rather than after. The procedure has genuinely changed, not just the paperwork.
The app
The Edition 4 tightness test, worked out for you
Flint has a tightness test tool built to Edition 4: put in the pipe runs and the meter, and it gives you the installation volume, the permissible drop for the gas you are on, the purge volume and a 1 + 1 + 2 timer. It was built from ISU 133 and IGEM's own FAQ after an engineer asked for it through in-app feedback.
Get Flint£3.99 a month, or £29.99 a year. Cancel any time.
Common questions
When does IGEM/UP/1B Edition 4 become mandatory?
Edition 4 is mandatory from 1 October 2026. Edition 3 is withdrawn on 30 September 2026.
What is the main change in Edition 4?
The permissible pressure drop is now set by the installation volume rather than by the meter size. That means working out the volume of the installation you are testing, from the meter and the pipework, before you know what drop is allowed.
Does a drop within the permitted limit still pass?
Not on its own. Any drop within limits has to be proved not to be in the pipework, by isolating every appliance and retesting, where there should be no perceptible movement.
Flint is a reference tool for competent, Gas Safe registered engineers. Everything here informs your judgement and never replaces it. Always work to the manufacturer's instructions and the current standards, and check every figure against the appliance data badge and manual.