Commissioning, Testing and Fault Finding
Commissioning sequence
Commissioning is a structured process: purge, pressure test, check operating pressure, verify gas rate, confirm combustion performance, and check safety devices. Candidates must know the order and why it matters; testing pressure before purging, for example, gives meaningless results. Traps include confusing test pressure with operating pressure, and forgetting to record results.
Pressure testing
Pressure testing verifies the integrity of new pipework before it is connected or commissioned. Know the test medium, the test pressure relative to operating pressure, the duration, and the acceptable pressure drop. A frequent trap is testing with the appliance connected when the standard requires isolation, or accepting a drop that exceeds the permitted allowance.
Fault finding
Fault finding should be systematic: confirm the symptom, isolate the cause by section (supply, pipework, controls, appliance), and verify the repair by retesting. Understand common faults such as blocked injectors, incorrect regulator setting, air in the line, faulty thermocouples, and flame failure device issues. Traps include replacing parts before diagnosing, and failing to re-verify combustion after a repair.
Worked example
A new appliance lights but the flame is unstable. Work from supply outward: check inlet pressure at the meter and at the appliance, confirm the regulator setting, inspect injectors and ports, then check the flame failure device. Only after correcting the cause do you re-run combustion checks and record the results.