The let-by, temperature stabilisation, and tightness test sequence for domestic properties.
Gas tightness testing confirms the integrity of the gas installation (including the meter, regulator, and pipework) to ensure there are no hazardous leaks. In the UK, domestic testing is governed by IGEM/UP/1B:
The Testing Sequence
- Visual Inspection: Inspect the installation, verify that the Emergency Control Valve (ECV) is open and all appliance isolation valves are closed.
- Connect Manometer: Attach a calibrated electronic or liquid (water/fluid) U-gauge manometer to the test point (usually on the gas meter or regulator outlet).
- Let-by Test (ECV check):
- Turn on the gas supply to pressurise the system to approximately 20 mbar.
- Turn off the ECV.
- Lower the pressure on the gauge slightly (to about 10 mbar or 15 mbar) to create a differential.
- Observe for 1 minute. Any rise in pressure indicates the ECV is letting gas by (passing gas when closed). The ECV must be replaced or repaired before a valid tightness test can proceed.
- Temperature Stabilisation:
- Open the ECV to re-pressurise the system to 20 mbar.
- Turn off the ECV.
- Wait 1 minute to allow the gas temperature inside the pipework to stabilise with the ambient room temperature.
- Tightness Test (2 minutes):
- Observe the manometer for 2 minutes.
- Under IGEM/UP/1B, for a standard domestic installation (with a diaphragm meter and no appliance connected/isolated), the maximum allowable pressure drop is 0 mbar (no drop). If appliances are connected and cannot be isolated, a small drop (typically up to 4.0 mbar) may be permitted under specific conditions, provided there is no smell of gas.
*Original revision guidance; verify testing values and allowable drops against IGEM/UP/1B.*