Gas Tightness Testing: Where an Ed. 3 Pass Becomes an Ed. 4 Fail

Examples of installations that Edition 4 is stricter on

U6 meter systems with more than a short run of pipe

A U6 meter holds 8 litres on its own, so a U6 job starts most of the way to the 10-litre line before you’ve added any pipework volume. If it includes roughly 13m of 15mm, or 6m of 22mm, you’re over the band and the permissible drop falls from 4 mbar to 2.5 mbar.

Say a two-bed home has 2m of 22mm to a tee, 6m of 15mm to the boiler and 3m of 15mm to the hob. That’s 2.09 L of pipework and fittings, plus 8 L for the meter, so 10.09 L in total. It’s over the line by less than a tenth of a litre.

A 3 mbar drop on that job would have passed under Edition 3. Under Edition 4, it fails.

Bigger homes with long pipe runs

Once the installation volume on a U6 job goes over 15 L, the permissible drop is 1 mbar. Pipe size makes a big difference here, because larger bores hold far more gas per metre. You’d need around 45m of 15mm to get there, but only about 20m of 22mm or 12m of 28mm.

Say a four-bed home has 10m each of 28mm, 22mm and 15mm. The pipework and fittings come to 11.0 L. Add the U6 and the installation volume is 19.0 L.

A 2 mbar drop on that job would have sat comfortably inside the old 4 mbar limit. Under Edition 4 the limit is 1 mbar, so that drop is double what’s allowed.

Larger properties with an E6 meter

E6 ultrasonic meters hold about 2.4 litres, against the U6’s 8. Under Edition 3 they were allowed 8 mbar. Under Edition 4, an E6 job keeps that 8 mbar only while the installation volume stays at 5 L or under, which means less than about 7m of 22mm or 17m of 15mm.

For example, a three-bed home with an E6 meter, 8m of 22mm and 10m of 15mm has an IV of 6.76L. Its limit halves from 8 mbar to 4 mbar.

A 6 mbar drop on that job would have passed comfortably under Edition 3, but under Edition 4, it fails. On a bigger system, the gap only widens.

This also means the meter type matters more than it used to. In the two-bed example, the same pipework is allowed 2.5 mbar with a U6 and 8 mbar with an E6. If the meter has been swapped since your last visit, the allowed drop changes with it.

LPG systems with longer pipework

On LPG installations with no meter, Edition 3 allowed 1.5 mbar. Under Edition 4, anything over 2.5 L of installation volume, or about 16m of 15mm, is allowed 1 mbar. Over 10 L, there’s no allowance at all: the test needs no perceptible movement.

Above: The installation volume calculator and tightness test helper in the GES app.