Five free practice questions on gas appliances: module 9 of the nine modules of Ontario's Gas Technician 3 (G3) certificate exam, which TSSA runs. The exam is all multiple choice; these have four options and one correct answer, as every question in our bank does. Answer each one before opening the explanation. No account, no email.
01The questions
-
Which feature makes a gas appliance direct vent rather than power vent?
- It uses a fan to push its flue gases out through the vent
- It can vent horizontally through an outside wall of the house
- Its combustion air all comes from outdoors in a sealed pipe
- It has a draft hood that lets room air into its vent pipe
Show the answer
C. Correct. A direct-vent appliance gets all its combustion air directly from outdoors and vents its products directly outdoors through enclosed passageways connected to it. A power-vent appliance normally takes its combustion air from the space it is installed in.
Why not the others
A. A power-vent appliance does this too: its fan pushes the products through the vent. A fan alone does not make an appliance direct vent; where the combustion air comes from does.
B. Power-vent appliances also commonly terminate through a side wall, so a wall termination does not tell the two apart. The difference is the sealed outdoor air supply of the direct-vent type.
D. A draft hood belongs to a natural-draft appliance, which takes dilution air from the room into its vent. A direct-vent appliance is sealed from the room and has no draft hood.
-
A burner whose own blower pushes all of its combustion air into it under pressure is
- an inshot burner on a fan-assisted furnace
- a ribbon burner
- an infrared burner
- a power burner
Show the answer
D. Correct. A power burner has a blower that delivers the combustion air under pressure to the burner head, so it does not depend on gas-jet injection or on chimney draft; residential condensing boilers commonly use one.
Why not the others
A. A fan-assisted furnace's inducer sits after the heat exchanger and pulls the products out to the vent; its inshot burners still draw their primary air in with their gas jets, so they are not power burners.
B. A ribbon burner is an atmospheric burner named for its continuous ribbon of closely spaced ports, which gives a long unbroken flame. It does not have its own combustion-air fan.
C. An infrared burner heats mainly by radiation from a glowing ceramic or metal surface. Its mixture is usually induced like an atmospheric burner's, not driven by a fan as described.
-
In an intermittent-pilot system working normally, what ends the sparking during a trial for ignition?
- The main gas valve opening to the burner
- The module sensing the pilot flame
- The thermocouple heating up at the pilot
- The thermostat reaching its set point
Show the answer
B. Correct. Spark and pilot gas start together; when the module's flame-rectification circuit senses the pilot flame, it stops the spark and then opens the main valve. If no flame is sensed, the trial ends on its timer.
Why not the others
A. The main valve opens only after the pilot has been proven, and the spark has already stopped by then. Its opening is a result of the pilot proof, not what ends the spark.
C. Intermittent-pilot modules prove the pilot by flame rectification through a rod, not with a thermocouple, which belongs to standing-pilot controls.
D. The thermostat ends the whole call for heat, long after ignition. Sparking stops within the trial, as soon as the pilot flame is proven.
-
A furnace's combination gas control sits between the gas connector and the burner manifold. Which group of functions does it combine in one body?
- A manual on-off control, the automatic valves and the appliance regulator
- The room thermostat, the high-temperature limit and an automatic valve
- The appliance shut-off valve, the sediment trap and the service regulator
- The ignition control module, the flame sensor and a manual on-off control
Show the answer
A. Correct. The combination gas control puts a manual on-off control, the automatic valves the control circuit opens (pilot and main, or main alone on a direct-ignition appliance) and the appliance pressure regulator in one body, with inlet and outlet pressure taps. When the control circuit opens, its automatic valves close.
Why not the others
B. The thermostat and the high limit are separate switches in the control circuit. They decide when the gas control's automatic valve may open, but they are not part of the valve body.
C. The manual shut-off valve and the drip or sediment trap belong to the supply piping upstream of the appliance, and the service regulator sits at the meter. None of them is inside the combination gas control.
D. The ignition module and the flame sensor prove the flame and tell the gas control when to open. They are separate components wired to it, not parts of the valve body.
-
Cleaning the venting of a natural-draft boiler, a G.3 finds a motor-driven damper in the vent just above the draft hood, wired by a harness to the boiler's control. On the next call for heat, what must happen at this damper before the control starts the pilot?
- It stays closed until the pilot flame is proven, to save heat
- It opens partway, then fully once the main flame is proven
- It opens once hot flue gas from the main burner reaches it
- It drives fully open and its end switch proves it open
Show the answer
D. Correct. A vent damper closes during off cycles to cut heat loss up the vent. On a call for heat the control drives it open and starts the pilot trial only when the damper's end switch proves it fully open. The maker warns that a damper that is not fully open lets products such as carbon monoxide escape into the house, which is why the damper and its harness are never bypassed.
Why not the others
A. A closed damper is what saves heat between cycles, but lighting the pilot and then the main burner against it would send the products out of the draft hood into the room. The control holds off ignition until the damper is fully open and proven.
B. Ignition does not start with the damper part-open. The maker's sequence waits until the damper has opened completely and its end switch has made the circuit, and only then begins the pilot trial; the damper stays open while the burner fires.
C. This damper is motor-driven and wired to the control, which drives it open on the call for heat, before any gas flows. Waiting for hot flue gas to reach it would mean lighting the burner against a closed vent.
02Answer key
| Question | Answer | Learning outcome |
|---|---|---|
| Q1 | C | Natural draft, fan-assisted, power-vent and direct-vent appliances |
| Q2 | D | Burner types and uses: inshot, upshot, ribbon, ported, infrared, power burners |
| Q3 | B | Ignition sources: spark and hot-surface igniters |
| Q4 | A | Manual and automatic gas valves; the combination gas control |
| Q5 | D | Vent system parts: draft hood or draft control device, vent connector, B vent, chimney, liner, termination |
03What module 9 covers
The gas appliances a G.3 works on: appliance types and input ratings, natural-draft, fan-assisted, power-vent and direct-vent appliances and Ontario's limits on where they may go, burners and flames, pilots, igniters and flame sensing, gas valves, regulators, operating and limit controls, venting, draft and air supply, converting between natural gas and propane, and shutting an appliance down, cleaning it and putting it back into service.
TSSA names module 9 “Introduction to Gas Appliances”. It gives its G3 curriculum only to accredited training providers, so the seven objectives below are TicketPrep's own, built from public sources such as college course outlines and Ontario's regulations, not TSSA's. TSSA does not publish the G3 question count or how many exam questions come from each module: its prep guide gives no G3 count and no per-module count, and candidates who fail get a mastery report broken down by module. The right-hand column is how many questions our bank holds on each objective, Standard and Advanced together, not a count from the exam.
| Our objective | In our bank |
|---|---|
| Objective 9.1 Identify gas appliances, their ratings and where they may be installed | 9 |
| Objective 9.2 Describe burners and flames | 11 |
| Objective 9.3 Describe pilots, ignition systems and flame sensing | 14 |
| Objective 9.4 Describe appliance controls and safeties | 11 |
| Objective 9.5 Explain venting, draft and air supply | 15 |
| Objective 9.6 Describe converting an appliance between natural gas and propane | 6 |
| Objective 9.7 Shut down, clean, lubricate and reactivate an appliance | 6 |
04What the questions turn on
What the flame is telling you
Soft, yellow, sooty flames with lint on the air openings mean too little primary air. Noisy flames lifting off the ports, with the manifold pressure above the plate setting, mean overfiring from a regulator set too high. If the input is low while the pressure and the gas match the plate, the orifices are the suspect, often partly blocked by debris knocked loose during burner work.
Flame sensing needs a complete circuit
Flame rectification runs from the rod, through the flame, to the burner and back to the control through the burner ground. A broken ground wire leaves no flame signal even with a good flame, and a rod shorted to the burner passes no rectified current, so the control sees no flame. On a standing pilot, the knob is held until the thermocouple is hot enough to hold the safety magnet.
Spillage has a cause
Natural draft is buoyancy: hot flue gas is lighter than cooler outdoor air. A cold vent can spill for the first minute or so of a cycle and then draft normally; spillage that persists points to a blocked vent or a depressurized room. If a heater spills only when exhaust fans run, the remedy is to supply the air they remove. A spill switch that keeps tripping is never bypassed; the reason for the spillage is found.
Converting, and who lights it first
Propane carries more heat per unit volume and burns at a higher manifold pressure, so a conversion kit fits smaller orifices and a new regulator spring; a manifold reading still at the natural gas setting means the regulator was missed. The first lighting of a newly converted appliance is not G.3 work, but a signed-off G.3 under general supervision may relight it after that.
05The other modules
The G3 exam covers nine modules, 1 to 9. Each has its own page of free questions:
The TSSA G3 practice test page describes the full question bank. How these questions are written and checked: how our questions are made. Found a mistake? Tell us and we will fix it.