Domestic Gas Appliances: Installation, Commissioning and Servicing
What the exam tests
Installation, commissioning and servicing of domestic gas appliances. Questions cover pre-installation checks, operating pressure and gas rate, combustion performance, safety devices and the difference between a service and a safety check.
Core rules
- Before installation, check the appliance is suitable for the gas type, input, room, flue and ventilation; read the rating plate and the manufacturer's instructions.
- Commissioning includes purging the appliance, checking operating pressure at the correct test point, measuring gas rate, confirming flame supervision and other safety devices, and carrying out combustion analysis where required.
- Never adjust the meter regulator or appliance governor to compensate for undersized pipework. Low pressure at the appliance points to a supply problem to be diagnosed.
- Servicing follows the manufacturer's schedule: clean, inspect, replace worn parts, test safety devices and record combustion readings.
- A safety check is not a service; it is a limited visual and functional check. Do not describe one as the other.
Worked example
A boiler lights but the installer measures 17 mbar at the appliance test point while the meter outlet is 20 mbar. The gas rate is also below the rating plate figure. Instead of turning up the regulator, he checks the pipe size and finds a long 15 mm run with several elbows. The pressure loss is excessive. He corrects the pipework, then rechecks pressure and gas rate. The reasoning: pressure loss between meter and appliance is an installation defect, not a governor setting.
Marks-losing traps
Commissioning without a combustion check on a condensing boiler; using the meter test point as the appliance operating pressure; servicing without testing flame supervision; leaving the appliance on a temporary gas supply.