An ordered routine for isolating an appliance and proving it sound again before use.
Isolating an appliance properly, then proving it safe again before use, is a routine examiners expect you to follow without gaps:
- Identify the correct isolation point for the appliance and confirm what else it might affect.
- Turn off the gas at the appliance isolation valve, and use the emergency control valve where appropriate for the task.
- Prove the supply is actually off before you break into any pipework.
- Cap or plug open ends so that, if gas were present, it could not escape into the room while you work.
- Carry out the work within your competence, using suitable jointing and components.
- On completion, carry out a tightness test to prove the installation is gas sound before reintroducing gas.
- Relight, recommission and check the appliance operates correctly, including its safety devices.
The principle is simple: never rely on memory or assumption about whether gas is present. Prove it off before you open the pipe, and prove it sound before you put it back into use.