Gas Pressure Testing: Soundness Tests, Tightness Tests & IGEM Procedures

Summary

Gas pressure testing is the final safety verification step in any gas installation, repair, or commissioning job. It establishes whether the gas supply pipework and fittings are leak-free before the system is energised. Every Gas Safe registered engineer must be competent in gas tightness testing — it is a mandatory requirement of the Gas Safety (Installation and Use) Regulations 1998 and the Gas Safe Technical Bulletin TB008.

In UK domestic practice, the procedures follow IGEM/UP/1C (Institute of Gas Engineers and Managers — Utilisation Procedure 1C), which provides the definitive specification for domestic gas installations. A tightness test must be carried out:

• After any new gas pipework is installed
• After any existing pipework is disturbed (joint opened, extension added, meter changed)
• As part of a Landlord Gas Safety Check (LGSC) annual inspection
• On commission of any new gas appliance

Understanding the test procedures, pressure limits, pass/fail criteria, and what to do on failure is fundamental knowledge for any Gas Safe registered engineer.

Key Facts

• Test pressure — natural gas: 20 mbar for the standard domestic let-by test (meter isolated, pressure applied and monitored). Some procedures use 1.5× working pressure (approximately 30 mbar) for new installations
• Test pressure — LPG (propane): 50 mbar. LPG (butane): 37 mbar. Note: LPG testing requires different test equipment and procedures
• Manometer type: U-tube manometer (water-filled) or electronic digital manometer. The manometer must be calibrated to read in mbar. An electronic manometer is more accurate and readable at low pressures
• Test duration: Domestic tightness test: observe for 2 minutes minimum after stabilisation. For new pipework systems, some procedures require a longer hold period (see IGEM/UP/1C)
• Pass criterion: No pressure drop observed on the manometer over the test period. A drop of 0.5 mbar or more is a fail
• Let-by test: Specifically tests whether the Emergency Control Valve (ECV) at the meter is seating correctly — meter valve closed, pressure applied, observed — any pressure rise (from gas let-by past the meter) indicates ECV failure
• Working pressure check: With all appliances on, the working pressure should not drop more than 1 mbar below the standing pressure. A greater drop indicates under-sized pipework or a supply pressure problem
• Never use a naked flame — Using a lighter or match to detect a gas leak is extremely dangerous. Always use approved leak detection fluid (soapy solution or proprietary detector fluid) or an electronic gas detector

Quick Reference Table

Detailed Guidance

Equipment Required

Before any gas pressure test, ensure:

• Calibrated manometer — Electronic digital manometer (Pocketed or similar) preferred for domestic use. Must be calibrated and in date. U-tube water manometer acceptable but harder to read at low pressures
• Flexible connection hose — To connect the manometer to the test nipple at the gas meter or isolation valve. Must be gas-rated and in good condition
• Leak detection fluid — Approved soapy solution in a squeeze bottle, or proprietary leak detector spray (Snoop, EasySeal detector). Never use washing-up liquid neat — it can corrode brass fittings
• Gas detector (electronic) — Catalytic bead or infrared gas detector for pinpointing leaks. Calibrated and in date
• PTFE tape and jointing compound — For remaking any failed connections

The Domestic Tightness Test (IGEM/UP/1C Procedure)

This procedure applies to natural gas domestic installations:

Step 1 — Visual inspection: Before applying any test pressure, carry out a visual inspection:

• Check all pipework for corrosion, mechanical damage, incorrect installation, or unsafe materials
• Check that all appliances are turned off at their controls (but not isolated at meter)
• Check that the installation pipe does not pass through any unsafe route

Step 2 — Connect manometer:

• Connect the manometer to the test point on the meter. The test point is typically a 1/8 inch BSP plug on the outlet side of the meter
• Ensure the manometer is properly connected and the hose is not kinked or damaged

Step 3 — Purge test point nipple:

• Briefly open the test point to purge any air from the connection. Close the test point and allow the manometer to stabilise with gas pressure. The standing pressure should read approximately 21 mbar

Step 4 — Let-by test (ECV check):

• Note the standing pressure on the manometer
• Close the Emergency Control Valve (ECV) at the gas meter
• Observe the manometer for 1 minute
• If the pressure remains stable or drops (gas consumed by tight appliances drawing down): the ECV is seating — continue
• If the pressure rises: gas is passing through the closed ECV (let-by). The meter must be reported to the gas transporter (National Gas / Cadent / Northern Gas Networks depending on region). Do not proceed — advise the customer that the system must be made safe

Step 5 — Tightness test of installation pipework:

• With ECV closed, slowly pressurise the pipework from the test point to 20 mbar if required (many meters maintain pressure — simply observe the reading)
• Observe the manometer for a minimum of 2 minutes
• Pass: No drop in pressure (or a drop of less than 0.5 mbar, which may be temperature-related in cold conditions)
• Fail: Pressure drops — a leak exists in the installation pipework

Step 6 — On failure:

• Open the ECV and restore gas supply
• Use leak detection fluid on all joints, connections, and fittings — start at the most recent work and work outward
• Use an electronic gas detector for concealed pipework (under floors, in voids)
• Once the leak is found, make the repair, then re-test from Step 2

Step 7 — Pass — working pressure test:

• Open the ECV and allow standing pressure to stabilise
• Turn on all gas appliances simultaneously (all hob burners, oven, boiler, etc.)
• Observe the manometer under working load — the working pressure should not drop below 20 mbar (i.e., no more than 1 mbar below standing pressure)
• Fail (pressure drops excessively): Insufficient gas supply. Check pipe sizing — refer to IGEM/UP/2 (domestic pipe sizing) to confirm adequate capacity for the total load. May indicate meter/regulator fault or undersized pipework

Step 8 — Document results:

• Record the test results on the Benchmark commissioning sheet, the Landlord Gas Safety Record (LGSR), or on a job record sheet
• Record: standing pressure, working pressure, tightness test result (pass/fail), and any remedial actions taken

New Pipework Installation Testing

For new gas pipework installations (not just disturbance of existing), IGEM/UP/1C requires a strength test before a tightness test:

Strength test:

• Applied at 1.5× maximum allowable operating pressure (MAOP). For a 21 mbar natural gas system: approximately 30 mbar
• Hold period: minimum 1 hour
• Purpose: verify structural integrity of pipe and fittings — not just leak-free

Tightness test:

• After strength test passes, depressurise to working pressure and carry out the standard tightness test

This two-stage process is most relevant for new extensions or complete re-pipes. For routine appliance changes (connecting a new boiler, replacing a cooker), the standard tightness test alone is typically sufficient — confirm with IGEM/UP/1C for the specific scenario.

Landlord Gas Safety Check (LGSC)

The annual gas safety check required under the Gas Safety (Installation and Use) Regulations 1998 for rented properties includes a tightness test of the installation pipework. The procedure is the same as above.

The Landlord Gas Safety Record (LGSR) must be completed for each appliance checked, and the tightness test result recorded. Copies must be:

• Provided to the existing tenant within 28 days of the check
• Provided to a new tenant before they move in
• Retained by the landlord for 2 years

Unsafe Situations and ID Codes

Gas Safe TB008 provides immediate unsafe situation (IUS) codes for recording and communicating gas safety status:

A failed tightness test with a confirmed leak is an ID1 situation. The engineer must:

1. Turn off the gas at the ECV
2. Issue a Warning Notice (form GS(M)R Notice) to the customer/landlord
3. Label the installation (sticker) with the ID code and engineer details
4. Record on the job sheet and LGSR

The engineer must not leave a property with a confirmed gas leak unless the gas is off at the meter and the customer has been warned.

Frequently Asked Questions

My gas meter has no test point. How do I carry out a tightness test?

Older meters may not have a test point nipple fitted. Alternatives: (a) fit a temporary test point adaptor to the outlet union of the meter; (b) use a test point on the first isolation valve downstream of the meter. The test must be carried out downstream of the ECV — testing upstream is testing the incoming supply (National Grid's responsibility, not yours).

Can I carry out a tightness test for a tenant?

Yes — if you are Gas Safe registered in the appropriate category (Domestic Natural Gas). You must complete the Landlord Gas Safety Record and provide copies to the landlord and tenant as described. If you are not Gas Safe registered, you cannot carry out any gas work, including testing.

A joint I've just made is bubbling on the leak detection test. What do I do?

Turn off gas at the meter. Remake the joint: for compression fittings, this means disassembling and replacing the olive if possible, or tightening further (one quarter-turn at a time). For threaded joints, remove and re-apply PTFE tape or jointing compound. For soldered joints, resolder (drain and dry the pipe first). Re-test the joint after any repair.

How do I test for gas leaks in concealed pipework?

An electronic gas detector is the most effective tool for locating leaks in inaccessible pipework. Run the probe along the suspected route of the pipe (along skirting boards, through inspection hatches). The detector will alarm as it approaches the source. Once the general area is identified, if access is needed, open up carefully — do not use power tools near a suspected gas leak (spark risk).

Regulations & Standards

• Gas Safety (Installation and Use) Regulations 1998 (GSIUR) — Legal framework for all gas work in the UK

• IGEM/UP/1C — Domestic gas installation, tightness testing procedures (Institute of Gas Engineers and Managers)

• Gas Safe TB008 — Technical bulletin on unsafe situations and ID codes

• Gas Safe TB001 — Technical bulletin on tightness testing procedures

• IGEM/UP/2 — Domestic gas pipe sizing (for working pressure failure investigation)

• Gas Safe Register — Technical Bulletins — TB008, TB001 and all current technical guidance for registered engineers

• IGEM Publications — UP/1C and UP/2 — Definitive procedures for domestic gas installation and testing

• HSE — Gas Safety — Regulatory framework and enforcement guidance

• cooker connection — Gas cooker bayonet fitting and commissioning

• boiler servicing — Annual service including gas pressure checks

• gas safe registration — Gas Safe registration categories and requirements

• smell of gas — Responding to suspected gas leak call-outs