Fault Diagnosis and Repair
What you must know
A logical diagnostic process: gather symptoms, form hypotheses, test in a safe order, confirm the fault, repair, and re-commission. Common faults: no gas (supply, valve, meter), ignition faults (spark, flame supervision), poor combustion (air/flue), low pressure (undersized pipe, regulator), and control faults (thermostat, PCB). Understand flame supervision devices and the safety implications of bypassing or defeating them - never defeat a safety device. Distinguish appliance fault from installation fault.
Traps in questions
- Jumping to component replacement without confirming supply and pressure.
- Defeating or bypassing a safety device to "prove" a fault - never acceptable.
- Confusing appliance fault with installation fault (e.g. low pressure from undersized pipe).
- Forgetting to re-commission and record after repair.
Worked example / rule of thumb
Rule of thumb: Supply → safety → control → combustion. Work from the meter outward and from safety devices inward. If gas pressure is correct at the meter but low at the appliance, suspect pipework sizing or a blockage, not the appliance.
Key exam behaviours
Stems describe symptoms; the best answer follows a safe, ordered diagnostic path and never defeats a safety device. Choose "confirm and re-commission" over "replace and leave".
Emergency Procedures and Unsafe Situations
What you must know
Emergency response: make safe, ventilate, remove ignition sources, isolate gas, warn occupants, and escalate. Know the classes of unsafe situation (ID, AR) and the correct notices and actions for each. Understand gas escape procedure (no switches, no flames, ventilate, isolate at meter if safe, call the emergency line), CO alarm response, and fire/explosion precautions. Know when to cap off, when to isolate, and when to advise only. Reporting to the responsible person and recording are mandatory.
Traps in questions
- Using a phone or switch inside a gas-filled area - move away first.
- Issuing an AR notice when the situation is ID.
- Failing to inform the user/responsible person in writing.
- Assuming you can leave an ID situation after "advising" - you must make safe.
Worked example / rule of thumb
Rule of thumb: Smell gas? No flames, no switches, ventilate, isolate if safe, get out, call the emergency line. For CO: evacuate, ventilate, get medical help if symptoms, then investigate the appliance. Always record and notify.
Key exam behaviours
Emergency stems reward the safest first action. Choose "make safe and evacuate/ventilate" over "investigate" when gas is present. Match notice type to severity and always include written notification.