GPT Troubleshooting & Diagnostics 3 — Questions and Answers
Question 1: A technician is called to a residence where occupants smell gas but no leak is found with a detector. What non-gas source should be considered?
- Sewer gas (hydrogen sulfide) from a dry drain trap (Correct answer)
- Electrical arcing from a nearby panel
- Refrigerant leak from an HVAC unit
- Carbon monoxide from a blocked flue
Correct answer: Sewer gas (hydrogen sulfide) from a dry drain trap
Sewer gas containing hydrogen sulfide can produce an odor similar to mercaptan-odoized natural gas and is often mistaken for a gas leak.
Question 2: What does it mean when a gas regulator is 'creeping' or passing gas in lockup?
- The regulator is undersized for the load
- The regulator valve seat is worn or debris is preventing full closure (Correct answer)
- The downstream pressure is too low
- The inlet pressure exceeds the regulator's rating
Correct answer: The regulator valve seat is worn or debris is preventing full closure
Regulator creep occurs when the valve seat is worn or contaminated with debris, preventing the regulator from fully closing in lockup condition.
Question 3: When diagnosing low gas pressure at an appliance, the technician measures normal pressure at the meter but low pressure at the appliance. What does this indicate?
- The meter is over-registering flow
- There is a restriction or significant pressure loss in the piping between the meter and appliance (Correct answer)
- The appliance regulator is set too high
- The service line from the street has insufficient capacity
Correct answer: There is a restriction or significant pressure loss in the piping between the meter and appliance
Normal pressure at the meter but low pressure at the appliance indicates a restriction, undersized pipe, or excessive friction loss in the interior distribution piping.
Question 4: A technician suspects a gas odor is coming from a flexible corrugated stainless steel tubing (CSST) fitting. What is the proper first diagnostic step?
- Tighten the fitting and retest
- Apply an approved leak detection solution to all fittings and connections (Correct answer)
- Replace the CSST section immediately
- Pressurize the system to 10 PSI to confirm the leak
Correct answer: Apply an approved leak detection solution to all fittings and connections
Applying an approved leak detection solution to fittings allows visual identification of bubble formation at the leak point before any repairs are made.
Question 5: What is the significance of a 'half-inch water column' pressure drop specification during a gas system leak test?
- It is the maximum allowable pressure drop indicating the system is leak-free (Correct answer)
- It is the minimum pressure required to begin a leak test
- It represents the pressure at which combustion occurs
- It is the standard regulator outlet pressure for residential systems
Correct answer: It is the maximum allowable pressure drop indicating the system is leak-free
Many codes specify that a system passes a leak test if pressure does not drop more than 0.5 inches water column over the test period, indicating an acceptably tight system.
Question 6: A gas technician finds corrosion on a black iron pipe joint that has a small pinhole leak. What is the correct repair procedure?
- Apply pipe repair epoxy putty and pressure test
- Shut off gas, cut out and replace the corroded section with new fittings (Correct answer)
- Wrap the joint with gas-rated repair tape and monitor
- Tighten the fitting to compress the corrosion
Correct answer: Shut off gas, cut out and replace the corroded section with new fittings
Corroded pipe with an active leak must be shut off and the affected section cut out and replaced — temporary patches are not an acceptable repair for gas piping.
Question 7: A technician observes that a gas appliance flame is yellow and lazy rather than blue. From a gas supply perspective, what could cause this?
- Insufficient gas pressure at the burner (Correct answer)
- Excessive gas pressure at the burner
- The gas supply has been contaminated with inert gas
- The appliance orifice is too small
Correct answer: Insufficient gas pressure at the burner
A yellow, lazy flame often indicates insufficient gas pressure or primary air, causing incomplete combustion — low supply pressure is a gas-side cause.
GPT Troubleshooting & Diagnostics 3
A technician is called to a residence where occupants smell gas but no leak is found with a detector.
What non-gas source should be considered?