CENWAT Gas Safe Regulations & Commissioning 3 — Questions and Answers
Question 1: What is the commissioning sequence for a new gas central heating boiler installation?
- Complete gas tightness test, fill and vent heating system, commission controls, light and set up boiler per manufacturer instructions, flue gas analysis, complete Benchmark checklist (Correct answer)
- Light the boiler first, then check for leaks
- Fill the system before the tightness test
- Flue gas analysis is done before lighting the boiler
Correct answer: Complete gas tightness test, fill and vent heating system, commission controls, light and set up boiler per manufacturer instructions, flue gas analysis, complete Benchmark checklist
The correct commissioning sequence includes: gas tightness test first, fill and vent system, set system pressure, commission controls and programmer, light and set up boiler following the manufacturer's procedures, perform flue gas analysis, and complete the Benchmark logbook.
Question 2: What is the purpose of the Benchmark commissioning checklist?
- To provide a standardised record confirming the installation and commissioning has been carried out correctly and the appliance is safe to use (Correct answer)
- To register the boiler with the manufacturer for warranty
- To notify the local authority of the installation
- To record the engineer's Gas Safe registration details only
Correct answer: To provide a standardised record confirming the installation and commissioning has been carried out correctly and the appliance is safe to use
The Benchmark checklist is a nationally recognised commissioning record that confirms all key installation and commissioning steps have been completed, supports warranty, and provides the homeowner with a record of the installation.
Question 3: What must be explained to the homeowner during handover of a new boiler installation?
- How to use all controls (programmer, thermostat, TRVs), how to check and adjust system pressure, what to do in an emergency, and when to arrange the first service (Correct answer)
- Only how to adjust the room thermostat
- Only the boiler's warranty terms
- Only the emergency shutdown procedure
Correct answer: How to use all controls (programmer, thermostat, TRVs), how to check and adjust system pressure, what to do in an emergency, and when to arrange the first service
A thorough handover includes instruction on all system controls, pressure checking, frost protection, emergency procedures, annual service requirements, and the completed Benchmark logbook handed over to the occupier.
Question 4: What is the purpose of setting the gas rate during boiler commissioning?
- To verify the boiler is consuming gas at the manufacturer's specified rate, confirming correct burner operation and heat output (Correct answer)
- To set the gas pressure at the meter
- To measure flue gas temperature
- To set the central heating flow temperature
Correct answer: To verify the boiler is consuming gas at the manufacturer's specified rate, confirming correct burner operation and heat output
Checking the gas rate using the gas meter (counting the dial or using a gas analyser) confirms the boiler is operating at its specified input, ensuring correct heat output and efficient combustion.
Question 5: What action should be taken if CO is detected in a habitable room during a gas safety inspection?
- Treat as an immediately dangerous situation: evacuate, ventilate, isolate the gas supply and investigate the source before re-entering (Correct answer)
- Increase room ventilation only
- Adjust the boiler controls and recheck
- Only act if CO exceeds 300 ppm
Correct answer: Treat as an immediately dangerous situation: evacuate, ventilate, isolate the gas supply and investigate the source before re-entering
CO in a habitable space is a life-threatening emergency; the property must be evacuated, the gas supply isolated, the property ventilated, and the source of CO identified and made safe before re-occupancy.
Question 6: What is the purpose of a flue flow test on a natural draught open-flued appliance?
- To confirm that the flue is drawing correctly, taking flue gases away from the appliance and out of the building (Correct answer)
- To measure flue gas temperature
- To check flue gas CO2 levels
- To test for gas leaks in the flue joints
Correct answer: To confirm that the flue is drawing correctly, taking flue gases away from the appliance and out of the building
A flue flow test (using smoke match or smoke pellet) confirms that the natural draught is sufficient to carry flue gases through the flue and away from the building, rather than spilling back into the room.
CENWAT Gas Safe Regulations & Commissioning 3
What is the commissioning sequence for a new gas central heating boiler installation?