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How to carry out a tightness test with a gas test gauge?

How to carry out a Tightness Test with a Gas Test Gauge?

Using a gas test gauge to test a device

A gas tightness test, which examines the gas pressure inside a property’s pipework, is a key part of a thorough gas safety test. It will ensure that there aren’t any gas leaks in the system.

Step 1 – Connect the Gas Test Gauge

Connect the gas test gauge to your gas meter. To ensure the accuracy of the readings ensure that your gas test gauge is zeroed first.

Step 2 – Open the Supply Valve

Open the supply valve of the meter until the pressure increases to approximately 10 mbar. Then, close the valve.

Step 3 – Observe the Gas Test Gauge for 1 Minute

Using a gas test gauge to test a device

Wait for 1 minute and observe the gas test gauge. There should not be any perceptible movement of the water in the u-tube.  


If the pressure rises, it demonstrates that the supply valve is not fully stopping the gas from leaving the meter; it is ‘letting-by’.

The valve will need to be checked further. You should spray leak detection spray into the valve to double-check if it is letting-by.


Gas let-by will be indicated by bubbles forming around the supply valve. If a leak is detected, the supply valve should be repaired or replaced by a qualified gas safe engineer.

Step 4 – Slowly Open the Valve to 20mbar

If, however, there is no let-by, slowly open the supply valve and increase the pressure until the gas test gauge reads 20 mbar. Then, close the valve.

Step 5 – Wait 1 Minute

Allow another minute for temperature stabilisation. This is a period of time in which the gas expands or contracts and adapts to the temperature environment within the pipework. Following 1 minute, if the pressure has dropped slightly, readjust the pressure to 20 mbar by opening the supply valve.

Step 6 – Observe the Gas Test Gauge for 2 Minutes

Using a gas test gauge to test a device

Observe the gas test gauge over the next two minutes. 


During this time, there should be no pressure drop. If a drop has occurred, close the appliance isolation valves on the meter to confirm that the meter itself is not leaking and the drop is, instead, due to a faulty gas appliance. 


No drop is allowed in the system pipework if the isolation valves are closed.

Step 7 – Observe the Gas Test Gauge for 2 Minutes

Following a successful test, remove the gas test gauge and reseal the gas test point on the meter.


Re-open the inlet supply valve and apply leak detector spray to the test point and all pipework before the valve to the supply pipe to double-check that there isn’t a leak.

The What and Why of Gas Testing Equipment

Gas testing equipment is a must-have for qualified and registered gas safe engineers. It is used to check if any gas is being leaked from gas pipework or appliances. 


This is necessary when you have a suspected gas leak but also when any new gas installation is about to be signed off as completed, especially before it will be distributed throughout a system making the location of the leakage much more difficult to locate.

The Law on Gas Testing Equipment

The law is specific in that it states common gas appliances including boilers and cookers must be gas safe certified and the testing has to be carried out by a qualified gas safe registered engineer and therefore gas testing equipment should likewise be used by certified engineers.


Types of Gas Test Gauges



These work by allowing gases to diffuse through a membrane that has a porous composition. It then passes an electrode which will be chemically oxidized or sometimes reduced. The identification and amount of gas is configured by how much gas is oxidized by the electrode. Simple but effective. 


Catalytic bead (pellistor)

This is the type of sensor most commonly used to detect combustible gases that present the potential hazard of exploding. Beads are situated at opposite arms of the Wheatstone bridge circuit. As they are heated up the catalysts, containing combustible compounds, will oxidize. The difference between the active and passive beads with identify how much gas is present. 



Photoionization detectors (PIDs) are able to detect gas and it’s concentration levels by making use of a high-photon-energy UV lamp. 


Infrared point

Infrared (IR) point sensors and depending on how the concentration and type of gas, the sensor beam with being absorbed. By determining how it is absorbed, the sensor determines which gas is present and how concentrated the gas is. 




Semiconductor sensors the chemical reaction that occurs when gas comes into contact with the sensor, often tin, to identify and measure the gas.


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