Since 1 October 2026, IGEM/UP/1B Edition 4 is the only edition there is. Edition 3 was withdrawn on 30 September, after six months of running side by side, so every tightness test and direct purge on a small installation is now done to Edition 4.

The headline change is simple to say and easy to get wrong on the day: the pressure drop you’re allowed now depends on the installation volume, not the meter size. There’s also a new step when the gauge moves, and a new way of working out the purge. None of it is hard. It just means a bit more to work out, and a bit more to write down.

What changed on site

The installation volume sets the drop you’re allowed

Add up the meter, the pipework and 10% of the pipework for fittings. For pipework you can’t see, estimate the length and assume the biggest size you know is in there. Then look the permissible drop up for that volume and gas in the standard’s tables. The meter’s badge no longer decides it.

The scope is tighter in number, wider in places

UP/1B covers installations up to 0.035 m³, a meter up to 16 m³/h, pipe up to 35 mm and 2 bar at the ECV outlet. Above that you’re on IGEM/UP/1A. Caravans and leisure accommodation vehicles are now covered too.

”No perceptible movement” now has a number

Up to 0.25 mbar on a water gauge, or 0.2 mbar on an electronic gauge reading to one decimal place. Anything more is movement.

The test itself

A let-by test first, then one minute to stabilise and two minutes on test. A pass means no perceptible movement, or a drop within the limit once the pipework is proven, and no smell of gas.

Gauge moved? Retest the pipework on its own

This is the step that’s new. The allowance is there for the bit of gas existing appliances let through. It is never an allowance for the pipework.

The allowance is for the appliances, never the pipework

1
Test with the appliances connected

Gauge moved?

Yes
Go to step 2

No
Pass, if there is no smell of gas
2
Isolate the appliances, retest the pipework alone

Pipework moved?

Can't isolate one? Then the first test needs no perceptible movement at all.

No
Go to step 3

Yes
Fail: trace and repair, or make it safe
3
Compare the first drop with the limit for the installation volume (IV)

Within it
No smell: pass

Over it
Fail

Any perceptible movement on the pipework alone is a fail, whatever the limit says.

Can’t reach 20 mbar on natural gas?

Isolate it and find out why first. Edition 4 lets you test from 18 mbar, but if it passes at that, check the operating pressure to IGEM/G/13 afterwards.

Purge volume is always worked out now

The assumed volumes for small installations have gone. Purge volume is 1.5 × the installation volume, every time. Natural gas up to 0.02 m³ of purge can go to air; above that, and on all LPG, purge to ignition.

And no going back

Once you’re working to Edition 4, you can’t switch to Edition 3 to turn a fail into a pass. A fail means trace and repair the escape, or make it safe.

What to write down now

Gas Safe Register recommends putting the edition you tested to on your work record. With the retest in the picture, a good record now holds:

the standard and edition: IGEM/UP/1B Edition 4
the installation volume, and how you got to it
the permissible drop for that volume and gas
the gauge you used
the first reading, and the pipework-only reading if you retested
the purge volume, and whether it went to air or ignition

If a job is ever questioned, “it passed” isn’t much of an answer. Two readings and the sum behind them are.

How Mucka handles it

The sums, done for you. Tell the installation volume calculator what the meter is and list the pipe runs: a size and a length each. It adds the 10% for fittings and gives you the installation volume, the purge volume, whether to purge to air or ignition, and the drop you’re allowed from the Edition 4 tables. Go over 0.035 m³ and it tells you you’re on UP/1A, rather than quoting a limit that doesn’t apply. It works with no signal, because meters live in cellars, and you can just ask: “U6 meter, two metres of 22 and nine of 15, what drop am I allowed?”

One tap onto the record. From the Gas Testing & Purging record, tap Work it out, do the sum, and it fills the volumes, the limit and the purge figures in one go. The working is kept with the certificate and prints on the PDF. Change a figure afterwards and the record shows both your figure and the calculated one.

A record built for Edition 4. Every record says which standard it was tested to, Edition 4 by default, and that prints in the heading of the tightness test and the purge. There’s a place for the pipework-only retest: not needed, done (with the reading), or couldn’t isolate the appliances. Pick your gauge and Mucka reminds you where perceptible movement starts on it. Test natural gas under 20 mbar and it mentions the 18 mbar floor and the G/13 check.

Your call, always. Mucka gives you the limit and the reminders. It never marks a test pass or fail for you. That’s the engineer’s job, and it stays yours.

Talk it in. Hands full at the meter? Say “tested to UP one B, pipework retest done, pipework drop nought” and it goes in the right boxes.

Try it

Already on Mucka? Open a Gas Testing & Purging record from any job, or find the installation volume calculator under Calculators. Not on Mucka yet? Book a demo and we’ll run a tightness test record through with you.

This is a summary, not the standard. Keep a copy of IGEM/UP/1B Edition 4 to hand, and work to it.

Sources

IGEM: frequently asked questions on IGEM/UP/1B Edition 4
Installer Online: IGEM/UP/1B Edition 4, what installers need to know about the updated tightness test