TSSA Gas Technician 1 (G1) common mistakes
TSSA Gas Technician 1 (G1) · Understand the traps and how to avoid them.
Sizing a gas pipe run from a single table value without adding the pressure drop of every fitting, appliance connector, and manifold, then declaring the run acceptable.
Candidates memorize one capacity table (e.g., schedule 40 black iron at 0.5 in w.c. drop) and treat the longest length as the only variable, forgetting that equivalent length for elbows, tees, and valves must be added before entering the table, and that the allowable drop depends on supply pressure and appliance minimum inlet pressure.
What to do instead
Work the problem in a fixed sequence every time: determine available pressure (supply pressure minus appliance minimum inlet pressure minus any regulator drop), convert every fitting to equivalent length using the table in the code book, add it to the measured run, then enter the correct capacity table for the actual gas (natural vs. propane), specific gravity, and pressure drop. Show the arithmetic so a wrong table choice is visible.
Venting a Category I appliance into a common chimney or existing liner without verifying the appliance's listed vent category, the liner's suitability, and the combined input of all appliances sharing the flue.
Candidates conflate 'natural draft appliance' with 'can use any chimney', and skip the steps of checking the appliance rating plate for vent category, checking whether the existing liner is listed for the new appliance, and summing inputs to confirm the flue is not oversized or undersized.
What to do instead
Before approving any venting arrangement, read the rating plate for category and vent size, confirm the liner material and listing, total the connected input, and check the vent tables for the actual height, connector rise, and number of appliances. If any of those inputs is unknown, the correct answer is 'not acceptable as installed' rather than a guess.
Treating combustion air as satisfied because the mechanical room 'has a louver' rather than calculating free area, confirming the louver's free-area percentage, and checking whether the openings serve the required volume or the appliance input.
Code questions present a room with two openings and candidates assume any opening passes; they forget that louvered openings must be derated for free area (often 25–75 percent), that the 'indoor air' method has a volume-per-input threshold, and that a confined space needs two permanent openings sized to the total input.
What to do instead
Always compute: room volume versus the threshold for the total input, then either the indoor-air allowance or the required free area for each opening (with louver derating applied). State the free-area percentage you assumed and why. If the question gives louver dimensions without a free-area percentage, flag that as the deciding detail.
Diagnosing a no-heat call by replacing parts (thermostat, gas valve, igniter) before measuring flame sense current, proving the ignition sequence, and confirming gas pressure at the manifold.
Candidates answer from pattern recognition ('it's usually the igniter') instead of following the appliance's own sequence of operation, and they skip microamp measurement because it requires setting up a meter in series with the flame sensor.
What to do instead
Write the sequence of operation from the wiring diagram first (call for heat, inducer prove, ignition trial, flame prove, main valve hold), then identify which step fails and measure at that step. For flame sense, measure microamps in series and compare to the manufacturer's minimum; for gas, measure supply and manifold pressure under flow. The answer that names the measured value beats the answer that names a part.
Confusing lockout behaviour with recycle behaviour, and misidentifying which device (flame safeguard, high limit, rollout switch, pressure switch) caused the shutdown.
Candidates memorize 'it locks out' without learning that a rollout switch or manual-reset high limit requires manual reset, that a pressure switch that opens during operation typically recycles, and that the flame safeguard's own lockout timing depends on the control type. They also skip reading the diagnostic LED or fault code.
What to do instead
Build a table in your head with three columns: device, what it senses, and whether it is manual reset, auto recycle, or lockout. On any scenario question, first ask 'is the device in the safety circuit or the operating circuit?' and 'did it trip before or after flame was proven?' Then match the observed symptom to that table rather than to a remembered phrase.
Treating a thermocouple or thermopile test as a continuity check instead of a loaded millivolt measurement, and accepting an open-circuit reading as proof the device is good.
Candidates use a multimeter on the resistance or continuity setting because it is the familiar function, not realizing that a thermocouple can show correct open-circuit voltage and still fail under load when the closed circuit is completed through the valve operator.
What to do instead
Test under load: connect the meter in the circuit with the valve operator connected, hold the pilot/thermopile at operating temperature, and compare the closed-circuit millivolts to the manufacturer's specification (open-circuit values are only a screening step). Also measure the magnet/operator coil and the drop across each connection, since a corroded terminal can mimic a failed thermocouple.
Applying a clearance or code rule from memory without identifying which code edition and which authority having jurisdiction applies to the question.
The exam spans multiple code books (gas code, installation code, electrical code, appliance standards) and candidates answer with a rule they learned from a different edition or a different country's code, or they answer a clearance question with a venting rule.
What to do instead
For every code question, name the code and the clause you are relying on before choosing an answer, and check whether the question states an edition or jurisdiction. Where a clearance is asked, distinguish appliance clearance to combustibles (from the rating plate) from vent clearance to combustibles (from the vent listing) from code-mandated access and ignition-source clearances.
Ignoring the electrical schematic's ladder logic and answering control questions from wire colour or terminal numbering alone.
Candidates trace wires physically rather than reading the ladder, so they miss that a safety switch is wired in series with the valve operator, that a limit is in the thermostat circuit, or that a relay contact is normally closed. Colour codes vary between manufacturers and installations.
What to do instead
Redraw the circuit as a ladder from the diagram before answering: line voltage on one rail, neutral on the other, each switch and load in order. Then ask 'if this switch opens, which loads lose power?' That single question resolves most control and safety-device questions without relying on colour or terminal numbers.
Converting between pressure units and between gas quantities (cubic feet, cubic metres, BTUs, megajoules) with a remembered factor rather than a derived one, producing answers that are off by a factor of roughly 3.5 or 10.
Candidates mix imperial and metric tables, confuse in w.c. with psi, or use a heating value for the wrong gas. Under time pressure they pick the answer closest to a half-remembered number.
What to do instead
Carry the units through every calculation and cancel them explicitly. Memorize only the anchor conversions (1 psi ≈ 27.7 in w.c.; 1 in w.c. ≈ 249 Pa; 1 cubic foot ≈ 0.0283 m³) and derive the rest from heating value times volume. Sanity-check the result against the appliance input on the rating plate.
Answering a servicing scenario with a single corrective action when the question asks for the sequence of checks, or skipping the verification step after the repair.
Candidates see a familiar symptom and jump to the fix, treating the question as a vocabulary test. They also omit the post-repair steps (leak test, combustion analysis, draft verification, documentation) that the exam treats as part of the job.
What to do instead
For any troubleshooting question, structure the answer as: verify the complaint, inspect and test in sequence, isolate the fault, repair, then re-verify with measured values (gas pressure, draft, CO/CO2, flame signal) and document. Choose the answer that includes verification; if two answers both fix the fault, the one with the documented re-check is correct.