Question

Q. When doing a let-by test, what are you looking for?

(Gas utilisation, Level 3- Diploma in Plumbing and Heating)

Answer 1

Examines the gas pressure inside a property's pipe work, is a key part of a let-by test. It will ensure that there aren't any gas leaks in the system.

Step 1 - Connect gas test gauge to gas meter.Connect a zeroed gas test gauge to the testing point of your gas meter.

Step 2 - Open supply valveOpen the supply valve of the meter until the pressure increases to approximately 10 mbar.Then, close the valve.

Step 3 - Observe gas test gaugeWait 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 - Increase pressureIf, 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 for another minuteAllow 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 gas test gauge.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 - Remove gauge and reseal gas test point.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.