RGII 5-Year Competency Assessment cheat sheet

Gas work in domestic premises must be carried out by a competent person; notification to the HSE under RIDDOR applies to specified reportable gas incidents, including deaths and certain injuries.

Gas Safe Register registration is the legal requirement for businesses working on gas; the register replaced CORGI in 2009.

A Landlord Gas Safety Record (CP12) must be issued for rented domestic premises at intervals not exceeding 12 months, with a copy given to the tenant and a record retained for 2 years.

The Gas Safety (Installation and Use) Regulations 1998 cover installation, maintenance and use of gas appliances and flues in domestic and commercial premises.

Flue inspection and safety checks: the responsible person must ensure appliances and flues are maintained in a safe condition and checked for safety at intervals not exceeding 12 months in relevant premises.

Tightness testing and purging must follow recognised procedures (IGEM/UP/1 series for commercial, IGEM/UP/1B for domestic); a let-by and stabilisation period precedes the pressure-loss test.

Warning notices: an ID (Immediately Dangerous) situation requires the appliance to be turned off and labelled; an AR (At Risk) notice is used where operation could become dangerous.

Records must be kept for gas work performed, including test results, and RIDDOR reports for dangerous gas fittings must be made without delay.

Natural gas (methane, G20): gross calorific value approximately 38.7 MJ/m3; relative density about 0.6 (lighter than air); Wobbe index about 50.7 MJ/m3.

LPG (propane, G31): gross calorific value approximately 95.8 MJ/m3; relative density about 1.55 (heavier than air, accumulates at low level); Wobbe index about 73.5 MJ/m3.

Butane (G30): gross CV approximately 126 MJ/m3, relative density about 2.0; vaporises only above about -2 degrees C at atmospheric pressure, so is unsuitable for outdoor winter use.

Complete combustion of methane: CH4 + 2O2 -> CO2 + 2H2O; stoichiometric air requirement is about 9.5 volumes of air per volume of gas.

Incomplete combustion produces carbon monoxide (CO), a colourless, odourless, tasteless gas that binds haemoglobin about 200-250 times more readily than oxygen.

Odorisation: natural gas is odorised with a sulphur-based compound (typically THT) to give a distinctive smell detectable at about one-fifth of the lower explosive limit.

Flammable limits in air: methane approximately 5-15% by volume; propane approximately 2.1-9.5% by volume; butane approximately 1.8-8.4% by volume.

Ignition temperature: methane about 595-605 degrees C; propane about 450 degrees C; butane about 410 degrees C (autoignition in air).

Gas leak detection: a flammable gas detector calibrated for the gas, or leak-detection fluid, is used; a flame must never be used to search for leaks.

Complete combustion requires correct gas rate, adequate primary and secondary air, and a suitable flue to remove products; CO2 in flue products for natural gas appliances is typically 8-10% at correct combustion.

Excess air dilutes flue gases and lowers CO2 reading; insufficient air raises CO and can produce yellow, lazy flames and sooting.

Oxygen depletion and CO production: a CO/CO2 ratio above 0.004 indicates a potential problem; above 0.008 is generally treated as At Risk and above 0.02 as Immediately Dangerous (industry guidance).

Open-flued and room-sealed appliances require ventilation sized to the appliance input; adventitious air is not normally counted for open-flued appliances in modern dwellings.

Ventilation for natural gas appliances: permanent openings sized per manufacturer instructions and BS 5440-2; a typical rule is 5 cm2 free area per kW for open-flued appliances above 7 kW.

Flue flow and spillage tests are performed on open-flued appliances: a smoke pellet confirms flue pull, and a spillage test at the draught diverter confirms products clear under worst-case conditions.

Room-sealed appliances take combustion air directly from outside and must have a suitable terminal position clear of openings, per BS 5440-1 distances.

Combustion analysis uses a flue gas analyser measuring O2, CO, CO2 and temperature; the appliance must be at operating temperature and the sample taken at the manufacturer's test point.

Domestic natural gas installation pipework is typically medium pressure (up to 2 bar) or low pressure (up to 75 mbar); most domestic installations operate at about 21 mbar at the meter outlet.

Sizing uses pressure-loss tables (e.g. BS 6891 for domestic); permissible pressure drop from meter to appliance should not exceed 1 mbar for natural gas with a 2 mbar working pressure at the appliance.

BS 6891 covers low-pressure natural gas installations up to 35 mm nominal size; copper, steel and approved multilayer pipe may be used subject to the standard.

Sleeving: pipe passing through a wall or floor must be sleeved and sealed, with the sleeve vented where it passes into a cavity or void to prevent gas accumulation.

Jointing: compression fittings must be accessible and not buried; soldered joints on gas pipework are generally not permitted in domestic installations; threaded joints use approved jointing compound or PTFE tape.

LPG pipework runs externally in copper or steel; underground LPG pipework must be protected and sleeved; LPG vapour pipework is sized for the higher relative density and lower calorific volume.

Protection: pipework must be supported at intervals, protected against corrosion, and electrically bonded; equipotential bonding of the installation pipework near the meter is a requirement.

Purging of new pipework is required before commissioning; purging volume is calculated from pipe volume and must be done to a safe location, with the gas/air mixture vented away from ignition sources.

Tightness testing sequence: (1) let-by test at operating pressure, (2) stabilisation period, (3) pressure-loss test at test pressure for the specified duration, with no allowable drop.

Test pressures and durations follow IGEM/UP/1B for domestic: for a low-pressure installation, a test pressure of about 20-30 mbar with a 2-minute test (after stabilisation) is typical; commercial durations per IGEM/UP/1.

Operating pressure at the meter outlet for natural gas is nominally 21 mbar (range typically 19-23 mbar); appliance inlet pressure should be within manufacturer's tolerance.

Gas rate check: meter reading over a timed period compared with the appliance data badge input; a metric meter measures m3, an imperial meter measures cubic feet (1 ft3 = 0.0283 m3).

Commissioning includes: purge, tightness test, gas rate, operating pressure, combustion analysis, flue flow/spillage, ventilation check, and completion of the benchmark/commissioning record.

Appliance data badge gives model, gas type, category (e.g. II2H3P), input (kW), output (kW), and NOx class; the installer must confirm the appliance is suitable for the gas supply.

Flue terminal positions per BS 5440-1: e.g. a balanced flue terminal must be at least 300 mm from an opening window and 600 mm from a boundary or opposite wall (manufacturer instructions take precedence).

Electrical safety: the appliance must be correctly earthed and cross-bonded; polarity and resistance-to-earth checks are performed before energising controls.

Service frequency: appliances should be serviced per manufacturer instructions; annual servicing is typical for domestic boilers and is mandatory for rented property gas safety checks.

Service scope includes: visual inspection, flue integrity, combustion analysis, cleaning of heat exchanger and burner, checking gas pressure and rate, safety device function (flame supervision, overheat, pressure relief).

Flame supervision device (FSD) test: extinguish the flame and confirm the gas valve closes within the manufacturer's specified time (typically within 60 seconds for many domestic appliances).

Combustion analysis readings recorded at service: CO/CO2 ratio, CO ppm, O2%, CO2%; comparison against previous readings identifies deterioration.

Inspection of flues: check for integrity, correct support, adequate clearance, no blockage, and correct terminal position; a flue in a void must be visually inspected where accessible.

Safety checks on gas pipework: visual inspection for corrosion, adequate support, sleeving, and bonding; a let-by and tightness test is performed if pipework has been disturbed.

Records: service record, benchmark log, and CP12 (for rented) document the work; defects are recorded and the responsible person informed.

Ventilation check at service: confirm permanent vents are clear and correctly sized for the appliance; blocked vents are a common cause of CO production.

No heat / no hot water: check gas supply (meter, emergency control valve position), appliance isolation valve, gas rate, and operating pressure before replacing components.

Ignition faults: check spark electrode gap and condition, ignition lead continuity, and flame detection (ionisation or rectification) circuit; a poor earth causes intermittent lockout.

Overheat lockout: check pump operation, system pressure, air locks, and the overheat thermostat; a blocked heat exchanger or faulty diverter valve can cause repeated trips.

Gas valve faults: verify the valve receives the correct signal and that inlet pressure is present; do not adjust the valve unless the manufacturer permits and the correct procedure is followed.

Flame failure / lockout: distinguish between ignition failure and flame detection failure by observing the sequence; FSD faults often trace to a dirty or misaligned electrode.

Pressure and flow faults: low operating pressure at the meter indicates a supply issue (governor, service pipe) rather than an appliance fault; low appliance inlet pressure with correct meter pressure indicates a pipework restriction.

Combustion faults: high CO with low CO2 suggests incomplete combustion (air starvation, blocked flue, dirty burner); high CO2 with high CO suggests over-gassing or restricted air.

Electrical faults: use a multimeter to check continuity, resistance and voltage at test points; consult the manufacturer's wiring diagram; isolate and prove dead before working on electrics.

On discovering a gas escape: turn off the emergency control valve, extinguish all flames, do not operate electrical switches, open doors and windows, and evacuate; call the gas emergency service (National Gas Emergency Service 0800 111 999 in the UK).

Emergency control valve (ECV) is located at the meter; it is operated by turning the lever to the closed position (typically 90 degrees); the valve must be left accessible and labelled.

ID (Immediately Dangerous): a situation that poses an immediate risk to life or property; the appliance must be turned off, disconnected where necessary, labelled, and the responsible person informed; a warning notice is attached.

AR (At Risk): a situation that could become dangerous; the appliance may be left off or, in some cases, the user is advised not to use it; a warning notice is issued and the defect recorded.

Warning notices (e.g. Gas Safe Register warning/ID labels) must not be removed until the defect is rectified; the defect is recorded and reported to the responsible person.

Carbon monoxide alarm activation: treat as a potential CO incident; ventilate, evacuate, do not re-enter until declared safe, and arrange investigation of appliances and flues.

Suspected gas leak in a void or duct: do not enter without appropriate PPE and gas detection; ventilate and isolate at the ECV; escalate to the emergency service.

Reporting: dangerous gas fittings must be reported to the HSE under RIDDOR; the responsible person and, where relevant, the gas transporter must be informed.

Re-occupation: only after the source is found, repaired, and the installation passes tightness and safety checks; the ECV is reopened only when it is safe to do so.