Testing, Commissioning, Troubleshooting and Maintenance
This domain tests proving the job is right: pressure testing, purging, setting pressures, clocking input, combustion analysis, systematic fault-finding and a maintenance program that keeps the equipment safe between visits.
Pressure testing and purging
Test with air or inert gas - never oxygen or a flammable gas indoors - using a gauge sized so the test pressure is near mid-scale. Isolate the appliance, hold for the specified time and pressure, and soap-test every joint. Purge to a safe outdoor location, never into a confined space, and then prove the appliance lights correctly.
Commissioning measurements
Inlet and manifold pressure with the burner firing, clocked input at the meter, temperature rise, combustion analysis (O2, CO2, CO, stack temperature, draft) and ambient CO. Record everything; a commissioning sheet is both a deliverable and your defence.
Combustion interpretation
Natural gas complete combustion shows roughly 9–10% CO2 with excess air; propane's maximum CO2 is about 13.8%. High CO with high O2 means poor mixing; high CO with low O2 means insufficient air. CO air-free should stay below 100 ppm and far lower on condensing equipment. Altitude derating is about 4% per 1,000 ft above 2,000 ft.
Troubleshooting method
Confirm the complaint, verify the sequence step by step, test inputs before outputs, isolate to one component, repair, then re-test the whole system. Parts-swapping hides the cause and can leave a safety defect in place.
Maintenance
Filters, burners and orifices, flame sensors, heat exchangers, condensate traps, vent systems, water-heater flushing, boiler water treatment and record keeping.
Worked example
A water heater's 1 ft³ test dial turns once in 24 s with all other appliances off, and gas heating value is 1,000 Btu/ft³. Input = (3,600 ÷ 24) × 1,000 = 150,000 Btu/h, but the rating plate says 120,000 Btu/h - 25% overfired. Reasoning: a propane orifice in a natural gas appliance, excessive manifold pressure or a regulator passing are the likely causes; check the orifice first, then set manifold pressure with a manometer, then re-clock and re-analyze combustion.
Traps that cost marks
Clocking input with other appliances running; reading manifold pressure statically; quoting CO without converting to air-free; skipping draft; and releasing a system without a leak test record.