New Gas Safe Tightness Test Rules 2026
The CP12 Gas Safety Certificate Deadline
Why Your Rental Property Needs a Gas Safety Overhaul Before Winter
For years, landlords across Grimsby, Cleethorpes, and the wider North East Lincolnshire area have benefited from a bit of built-in leniency during annual gas safety checks. That leniency is now officially on borrowed time.
On 25th March 2026, the gas industry released IGEM/UP/1B Edition 4. This new standard fundamentally changes how engineers conduct tightness tests, effectively eliminating the safety net for weeping pipework. While there is a brief grace period running until 30th September 2026, waiting until winter to address this could mean unexpected failures, capped meters, and urgent repiping work during your next CP12 inspection. Here is what is changing and why it matters to your portfolio.
The Old Allowances vs. The New Two-Stage Test
Under the old rules, domestic gas installations were allowed a slight pressure drop during a test, provided there was no smell of gas. This allowance based entirely on your meter type and pipework size accounted for minor, historically “safe” weepages in older systems.
The new Edition 4 standard scraps the meter-size rule entirely, replacing it with limits based on the system’s Installation Volume (IV). But the biggest shift is how the test is actually performed:
- The Appliance Allowance: We first test the whole system. If there is a slight drop, we calculate the IV and check it against the new permissible limits. However, this allowance is strictly to account for minor let-by on existing appliance gas valves, not the pipework itself.
- The Pipework Reality: If the initial drop is within limits, we must now isolate every single gas appliance in the property and test the pipework again. During this second test, there can be no perceptible movement on the gauge. If the gauge drops, the test is an automatic fail.
In short: The gas pipework is no longer allowed to leak, period.
The Hidden Trap: Inaccessible Appliances
In the older Victorian and Edwardian terraces common across our local area, this introduces a massive logistical trap for landlords.
If an engineer cannot easily access an isolation valve, for example, one buried behind an integrated washing machine or built-in hob, the new rules state we must apply the strict ‘no perceptible movement’ criteria to the entire installation. If that un-isolatable appliance has a microscopic weep, the whole property fails the CP12, and the gas supply must be made safe.
What Landlords Need to Do Now
The gas industry is running a 6-month transition period where the old standards can still be legally applied, ending on 30th September 2026.
This means the summer is your strategic window. If your property has old threaded steel pipework, a dated gas fire, hidden isolation valves, or a history of “borderline” passes on previous certificates, you need to act now. Once October hits, the old rules are withdrawn. A failed test under the new rules means the gas gets capped off immediately, leaving your tenants without heating or hot water right as the cold weather hits, and right when heating engineers are at their busiest and hardest to book.
Don’t wait for a winter emergency. Use the summer to investigate your pipework, install accessible isolation valves, and future-proof your properties.
Interested in getting your properties up to standard before the rules tighten? iWarm are Gas Safe registered engineers serving North East Lincolnshire. View our Gas Safety Certificates page, learn about our Boiler Repairs in Grimsby or contact our team to get your rental portfolio sorted.
Check out the Gas Safe Register website if you would like more information on IGEM/UP/1B Edition 4 Tightness testing and direct purging of small Liquefied Petroleum Gas/Air, Natural Gas and Liquefied Petroleum Gas installations.
Frequently Asked Questions
Under the previous standard (Edition 3), domestic installations were permitted a small, calculated pressure drop across the entire system as long as no gas smell was detected. Under Edition 4, pipework is held to a strict zero-tolerance standard. While a minor pressure movement may be temporarily permitted to account for internal appliance components, isolating the appliances must result in zero perceptible movement on the test gauge. If the pipework alone drops pressure, the installation fails immediately.
If an isolation valve is inaccessible, such as behind built-in kitchen cabinetry, tiled-in pipework, or integrated appliances, the engineer cannot isolate the appliance from the pipework. Under the updated regulations, the entire installation (including the connected appliance) must then meet the strict “no perceptible movement” standard. Any trace let-by within that appliance will cause the entire property to fail the tightness test.
Under the Gas Industry Unsafe Situations Procedure (GIUSP), an unresolved gas leak on the installation pipework must be classified and made safe. If the leak cannot be located and rectified during the visit, the engineer is legally required to isolate and cap the gas supply to prevent unsafe operation, leaving the property without active gas services until remedial pipework repairs are completed.
Edition 4 was published on 25th March 2026, operating alongside the previous edition during a six-month transition period. The transition window closes on 30th September 2026. Starting 1st October 2026, all domestic and small commercial tightness tests must strictly comply with Edition 4.
For older terraces and conversions (common across Grimsby and Cleethorpes), landlords should arrange a proactive pipework survey ahead of the autumn rush. Key preparations include:
– Ensuring all gas appliances (hobs, boilers, fires) have accessible, functioning local isolation valves.
– Testing and repairing legacy threaded steel or concealed lead pipework that may carry minor weeping joints.
– Decommissioning disused or non-compliant secondary appliances (such as decorative gas fires) before annual certificate renewals.
