TSSA Gas Technician 3 (G3) common mistakes
TSSA Gas Technician 3 (G3) · Understand the traps and how to avoid them.
Memorizing the three pressure categories (low, medium, high) as raw kPa numbers without being able to place a given appliance or supply pressure into the correct band, then guessing on classification questions.
Candidates study the numbers as isolated facts rather than as a laddered scale, so under exam pressure they confuse the boundary values (for example mixing up where low pressure ends and medium begins) and cannot classify an unfamiliar value.
What to do instead
Build a one-page ladder: write each band with its lower and upper limit, then place 10 real examples (residential manifold pressure, appliance inlet pressure, test pressures) on the ladder. Practice classifying random kPa values until you can do it without the page.
Confusing the properties and behaviour of natural gas versus propane - relative density, heating value per cubic metre, and which one is heavier than air - and applying one fuel's characteristics to the other.
Both fuels appear throughout the code and appliance material, and candidates learn them side by side without a comparison structure, so the details blur together.
What to do instead
Make a two-column comparison table covering relative density (air = 1), typical heating value, odourization, and leak behaviour (rising versus pooling). Recite it from memory, then answer practice items by naming the fuel first before reasoning.
Treating complete combustion and correct air requirements as a single memorized sentence instead of being able to state the approximate air-to-gas ratio, the products of complete combustion, and the symptoms of incomplete combustion.
This content is often skimmed because it feels like background theory, but the exam tests it through applied questions about CO, yellow flames, and sooting.
What to do instead
Learn the combustion triangle plus the approximate air requirement for each fuel, and link each abnormal symptom (yellow tipping, lifting, sooting, CO production) to its cause. Practise explaining each symptom aloud in one sentence.
Reciting code clause numbers without knowing what the clause actually requires, or applying a remembered number to the wrong situation.
Candidates see clause references in study material and assume memorizing the number is the goal, but exam items are scenario-based and ask what must be done, not which number applies.
What to do instead
For each major topic (clearances, bonding, venting, testing), write the requirement in plain language first and attach the reference second. Test yourself by scenario: given a situation, state the rule and the reason behind it.
Mishandling clearance-to-combustible requirements - measuring from the wrong reference point, or forgetting that reduced clearances require a specified protection method and labelled instructions.
Clearance questions are usually presented as distances, so candidates focus on the number and ignore the conditions (what the distance is measured from, and what permits a reduction).
What to do instead
Draw a simple appliance-in-an-enclosure sketch and label every clearance dimension from its correct reference surface. Add a note beside each reduced clearance stating what protection and documentation it requires.
Skipping or mis-sequencing the required leak test and purge procedure - testing at the wrong pressure or duration, or failing to purge air from a new line before attempting ignition.
In the field, experienced workers often shorten these steps, and candidates carry that habit into the exam, forgetting that the test pressure, hold time, and purge are separately examinable.
What to do instead
Write the procedure as a numbered checklist with pressure, duration, and acceptance criterion for each step, and include the purge step explicitly. Rehearse it in order until the sequence is automatic.
Sizing pipe or tubing by habit or by what fits, instead of using the correct sizing tables with the actual load, length, and allowable pressure drop, and ignoring the effect of additional fittings and appliances.
Sizing tables have many inputs and candidates avoid them, relying on rules of thumb learned on the job that do not hold for longer runs or added load.
What to do instead
Work through 5–6 sizing problems end to end, writing down each input (total load, equivalent length including fittings, inlet pressure, allowable drop) before touching the table. Show the units at every step.
Confusing bonding with grounding, or believing the gas connector itself provides the electrical bond, and therefore missing the requirement to bond the gas piping system.
The two terms sound interchangeable and the piping is often installed near electrical work, so candidates merge the concepts and pick the wrong answer.
What to do instead
State the definitions separately and note the purpose of each (fault current path versus earth reference). Then write one sentence on why the flexible connector cannot serve as the bonding means, and review it before the exam.
Applying venting rules without checking the appliance category and vent configuration - for example treating a Category I appliance like a direct-vent unit, or ignoring the combustion air source when deciding vent termination location.
Venting is the most rule-dense domain, and candidates memorize termination distances without first identifying the appliance category and the air-supply method, which determine which rules apply.
What to do instead
Adopt a fixed decision order for every venting question: identify appliance category, then vent type, then air supply, then check clearances and termination. Practise on 10 scenarios, writing the four decisions before choosing an answer.
On appliance servicing items, jumping to a component replacement (thermocouple, gas valve) before completing the diagnostic sequence of confirming gas supply, ignition source, flame signal, and combustion air.
Field experience rewards fast part swaps, and candidates bring that shortcut to scenario questions that are actually testing ordered troubleshooting logic.
What to do instead
Learn a fixed diagnostic ladder (supply pressure, ignition, flame proving, air and venting, then controls) and answer servicing questions by walking the ladder in order, naming the test performed at each rung.