GPT Troubleshooting & Diagnostics 2 — Questions and Answers
Question 1: A technician notices a gas meter spinning continuously even when all appliances are shut off. What is the most likely cause?
- A defective pressure regulator upstream
- An underground leak between the meter and the building (Correct answer)
- A faulty meter reading mechanism
- High ambient temperature affecting meter calibration
Correct answer: An underground leak between the meter and the building
Continuous meter movement with all appliances off indicates gas is escaping somewhere between the meter and the building, pointing to an underground leak.
Question 2: When performing a pressure drop test on a gas distribution system, what does a pressure drop exceeding acceptable limits indicate?
- The regulator is set too high
- There is excessive flow demand on an undersized pipe
- There is a leak or significant restriction in the line (Correct answer)
- The test gauge is improperly calibrated
Correct answer: There is a leak or significant restriction in the line
An excessive pressure drop during a pressure test indicates either a leak allowing gas to escape or a blockage/restriction impeding flow.
Question 3: A customer reports their gas furnace ignites but immediately shuts off. The technician checks and finds the gas pressure at the appliance is within spec. What should be checked next?
- The thermostat wiring
- The flame sensor or thermocouple (Correct answer)
- The gas meter diaphragm
- The service regulator vent
Correct answer: The flame sensor or thermocouple
If ignition occurs but the appliance shuts off immediately, the flame sensor or thermocouple is likely dirty or faulty and not confirming the flame to the control board.
Question 4: Which diagnostic method is preferred for locating an underground gas leak without excavation?
- Applying soapy water to the ground surface
- Using a combustible gas detector probe along the soil surface (Correct answer)
- Pressurizing the line with air and listening for hissing
- Checking for dead vegetation patterns only
Correct answer: Using a combustible gas detector probe along the soil surface
A combustible gas detector probed along the soil surface can detect gas migrating upward from an underground leak without requiring excavation.
Question 5: A technician finds that a gas pressure regulator is 'locked up' and not allowing gas flow. What is the most likely cause?
- Excessive downstream pressure has closed the regulator
- The upstream supply pressure has dropped to zero
- The regulator vent is blocked, preventing diaphragm movement (Correct answer)
- The appliance load is too low for the regulator to open
Correct answer: The regulator vent is blocked, preventing diaphragm movement
A blocked regulator vent prevents the diaphragm from sensing atmospheric pressure reference, causing the regulator to lock up and restrict flow.
Question 6: During a leak investigation, a technician detects gas odor inside a building but no exterior source is found. What is the correct next step?
- Evacuate the building and shut off the gas supply at the meter (Correct answer)
- Apply soapy water to all interior fittings immediately
- Increase the system pressure to help locate the leak source
- Open windows and continue testing with all appliances running
Correct answer: Evacuate the building and shut off the gas supply at the meter
Detecting gas odor inside a building requires immediate evacuation and shutting off the gas supply at the meter before any further investigation.
Question 7: A gas line fails a standing pressure test after 30 minutes. The technician re-tests after allowing the pipe temperature to stabilize and it now passes. What was the likely issue?
- The pipe had a slow leak that sealed itself
- Temperature change caused pressure variation that mimicked a leak (Correct answer)
- The test gauge was defective
- Moisture in the line absorbed the test pressure
Correct answer: Temperature change caused pressure variation that mimicked a leak
Temperature changes in the pipe or test medium cause pressure fluctuations that can mimic a leak — allowing temperature to stabilize eliminates this variable.
GPT Troubleshooting & Diagnostics 2
A technician notices a gas meter spinning continuously even when all appliances are shut off.
What is the most likely cause?