ACS CCN1 Core Domestic Gas Safety Assessment — Questions and Answers

Question 1: What is the maximum permissible pressure drop between the gas meter outlet and any appliance in a domestic installation?

1 mbar (Correct answer)
4 mbar
2 mbar
0.5 mbar

Correct answer: 1 mbar

The maximum permissible pressure drop between the gas meter outlet and any gas appliance in a domestic installation is 1 mbar. This ensures that each appliance receives adequate gas pressure for safe and efficient operation. If the pressure drop exceeds 1 mbar, the pipework may need to be upsized.

Question 2: What is 'back-draughting' in a flue system and what causes it?

Condensation forming in the flue and dripping back into the appliance
Forward flow of flue gases being blocked by a bird's nest in the flue
Reverse flow of flue gases down the flue and into the room — caused by negative pressure in the building, stack effect, or external wind conditions (Correct answer)
Excessive draught causing the pilot light to blow out

Correct answer: Reverse flow of flue gases down the flue and into the room — caused by negative pressure in the building, stack effect, or external wind conditions

Back-draughting occurs when the pressure differential reverses, causing combustion products to flow down the flue into the room rather than up and out. It can be caused by extract fans, stack effect, or external wind conditions.

Question 3: Under the Building Regulations (Part J), what is the minimum clearance distance from a balanced flue terminal to an opening window?

300 mm (30 cm) below or horizontally, and 300 mm above for most appliances — exact distances depend on appliance type and flue type (Correct answer)
100 mm in all directions
1 metre from any opening, regardless of direction
No minimum clearance is required for balanced flue terminals

Correct answer: 300 mm (30 cm) below or horizontally, and 300 mm above for most appliances — exact distances depend on appliance type and flue type

Building Regulations Part J (Combustion Appliances) specifies minimum clearance distances from flue terminals to openings. For most balanced flue appliances, the minimum is 300 mm to the side or below an opening window.

Question 4: Under RIDDOR, who must a Gas Safe registered engineer report a dangerous gas fitting to?

The HSE (Health and Safety Executive) via the online RIDDOR reporting system (Correct answer)
The local fire brigade
The gas appliance manufacturer
The local authority environmental health department

Correct answer: The HSE (Health and Safety Executive) via the online RIDDOR reporting system

Under RIDDOR regulation 6(2), Gas Safe registered engineers must report any dangerous gas fitting to the HSE using the online reporting form at www.hse.gov.uk/riddor. The report must be made as soon as reasonably practicable. The gas transporter (e.g., National Gas Emergency Service) should also be notified if there is an immediate gas escape.

Question 5: What is the purpose of a flue gas analysis test carried out during commissioning of a gas boiler?

To verify the electrical connections are correct
To test the condensate drainage system
To check the gas supply pressure
To measure the carbon monoxide, carbon dioxide, and flue gas temperature to verify safe and efficient combustion (Correct answer)

Correct answer: To measure the carbon monoxide, carbon dioxide, and flue gas temperature to verify safe and efficient combustion

A flue gas analysis (FGA) measures the levels of CO, CO₂, O₂, and flue gas temperature in the products of combustion. This verifies that the appliance is burning efficiently and safely, with combustion products within acceptable limits. The CO/CO₂ ratio must be within safe limits (maximum 0.004 for most boilers).

Question 6: At what intervals must copper gas pipework be supported (clipped) in a domestic installation?

Support intervals are at the installer's discretion
Every 1.2 metres for horizontal runs and every 1.8 metres for vertical runs (15 mm copper) — per BS 6891 (Correct answer)
Only at changes of direction
Every 3 metres regardless of pipe size or orientation

Correct answer: Every 1.2 metres for horizontal runs and every 1.8 metres for vertical runs (15 mm copper) — per BS 6891

BS 6891 specifies support intervals for domestic gas installations. For 15 mm copper pipe, supports are required at maximum 1.2 m intervals on horizontal runs and 1.8 m on vertical runs. Correct support prevents sagging and joint stress.

Question 7: What type of thermostat is designed to shut off the gas supply to a boiler if the water temperature exceeds a safe limit?

Programmer timer
Room thermostat
Overheat thermostat (limit thermostat) (Correct answer)
Frost thermostat

Correct answer: Overheat thermostat (limit thermostat)

An overheat thermostat (also called a limit thermostat or high-limit thermostat) is a safety device that shuts off the gas supply to the boiler if the water temperature exceeds a predetermined safe limit (typically around 85-90°C). This prevents the system from reaching dangerously high temperatures and pressures. It is a non-self-resetting device that requires manual reset.

Question 8: What legislation specifically governs the installation, maintenance, and use of gas fittings in the UK?

The Building Act 1984
The Control of Substances Hazardous to Health Regulations 2002
The Electricity at Work Regulations 1989
The Gas Safety (Installation and Use) Regulations 1998 (Correct answer)

Correct answer: The Gas Safety (Installation and Use) Regulations 1998

The Gas Safety (Installation and Use) Regulations 1998 (GSIUR) are the primary regulations governing gas safety in domestic and commercial premises. They cover installation, maintenance, use of gas fittings, and the duties of landlords, gas suppliers, and gas engineers.

Question 9: What is the purpose of a draught diverter (draught break) fitted to an open-flued gas appliance?

To increase the flue draught to maximum
To filter particles from the combustion products
To regulate the gas pressure to the burner
To prevent excessive draught (down-draught or up-draught) affecting the burner and to allow dilution air to enter the flue (Correct answer)

Correct answer: To prevent excessive draught (down-draught or up-draught) affecting the burner and to allow dilution air to enter the flue

A draught diverter stabilises the draught conditions at the appliance by preventing excessive variations in flue pull from affecting the burner. It allows dilution air from the room to enter the flue, which helps to maintain steady combustion conditions. It also provides a point at which spillage of combustion products can be detected during a spillage test.

Question 10: What is the purpose of a gas meter bypass?

It is not a legitimate installation component — a bypass around a gas meter is illegal as it allows gas use without metering (Correct answer)
It is a safety valve that diverts gas during excess pressure events
It allows gas to continue during meter maintenance
It is a pressure regulator fitted parallel to the meter

Correct answer: It is not a legitimate installation component — a bypass around a gas meter is illegal as it allows gas use without metering

There is no legitimate purpose for a bypass around a gas meter in a domestic installation. Creating or using a meter bypass is a criminal offence as it enables theft of gas and creates serious safety risks.

Question 11: What should an engineer do if a gas appliance cannot achieve the correct working pressure during commissioning?

Do not commission the appliance and investigate the cause of the low pressure (Correct answer)
Inform the customer and leave the appliance in service at reduced input
Adjust the appliance gas valve to compensate for the low pressure
Commission the appliance and note the pressure deficit in the paperwork

Correct answer: Do not commission the appliance and investigate the cause of the low pressure

An appliance that cannot achieve its design working pressure must not be commissioned, as incorrect gas pressure leads to incomplete combustion, poor efficiency, and potentially dangerous operating conditions.

Question 12: What is 'purging' in the context of gas pipework?

The testing of a flue system for blockages
The process of displacing air or inert gas from pipework with gas (commissioning purge) or displacing gas with air or inert gas (decommissioning purge) (Correct answer)
The removal of debris from a gas main before commissioning
The cleaning of gas pipework using high-pressure water

Correct answer: The process of displacing air or inert gas from pipework with gas (commissioning purge) or displacing gas with air or inert gas (decommissioning purge)

Purging involves displacing one gas with another. Commissioning purge replaces air in new or repaired pipework with gas. Decommissioning purge replaces gas in pipework with air or inert gas before it is worked on or abandoned.

Question 13: What is the maximum penalty for carrying out gas work while not registered with Gas Safe Register?

A fine of up to £5,000
An unlimited fine and/or up to 2 years imprisonment (Correct answer)
A 6-month suspension from work
A fine of up to £1,000

Correct answer: An unlimited fine and/or up to 2 years imprisonment

Under the Gas Safety (Installation and Use) Regulations 1998, it is a criminal offence to carry out gas work without being Gas Safe registered. The maximum penalty is an unlimited fine and/or imprisonment for up to 2 years on indictment.

Question 14: What is the typical maximum working pressure drop between standing and working pressure at a domestic gas meter?

1 mbar
2 mbar (Correct answer)
5 mbar
0.5 mbar

Correct answer: 2 mbar

The maximum acceptable pressure drop between standing pressure (21 mbar, no load) and working pressure (all appliances on maximum) at the meter is typically 2 mbar. This means the working pressure should not fall below 19 mbar when all connected appliances are operating at full rate. A drop exceeding this may indicate an undersized service pipe or meter.

Question 15: What is a 'gas incident' that a Gas Safe engineer is required to report to the HSE?

Incidents only if caused by the engineer's own work
Only incidents on commercial premises
Only incidents resulting in death
Any death, injury, or near miss attributable to a gas fitting or appliance, including CO poisoning incidents (Correct answer)

Correct answer: Any death, injury, or near miss attributable to a gas fitting or appliance, including CO poisoning incidents

Gas Safe engineers are required to report to the HSE any incident involving death, injury, or dangerous occurrence attributable to a gas fitting or appliance, including CO poisoning. This is required under RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations).

Question 16: When a gas appliance is classified as 'At Risk', what must the engineer provide before leaving the premises?

A written warning notice with the customer's acknowledgement (Correct answer)
A verbal warning to the occupant only
An immediate notification to the Health and Safety Executive
A completed Gas Safe dangerous appliance report form

Correct answer: A written warning notice with the customer's acknowledgement

When an appliance is classified 'At Risk', the engineer must issue a written warning notice explaining the risk and obtain the customer's written acknowledgement that they have been informed of the danger.

Question 17: What is the Wobbe Index and why is it significant for gas appliances?

The calorific value of natural gas in kJ/m3
A measure of the interchangeability of gases — appliances are calibrated for gas with a specific Wobbe Index, and using gas outside this range causes inefficient combustion (Correct answer)
The maximum safe gas consumption of an appliance
A measure of gas pressure at the meter

Correct answer: A measure of the interchangeability of gases — appliances are calibrated for gas with a specific Wobbe Index, and using gas outside this range causes inefficient combustion

The Wobbe Index quantifies the interchangeability of gas types. Appliances are designed for gas within a specific Wobbe Index range. Using gas outside this range disrupts the air-to-gas ratio, causing incomplete combustion or appliance malfunction.

Question 18: When checking for gas leaks at a meter connection, which method should be used?

A naked flame held close to the joint
Soapy water made from household washing-up liquid
A thermal imaging camera
Approved leak detection fluid (LDF) applied to joints and connections (Correct answer)

Correct answer: Approved leak detection fluid (LDF) applied to joints and connections

Approved leak detection fluid (LDF) conforming to BS EN 14291 must be used to check for gas leaks at meter connections and joints. The fluid is applied to suspected leak points and will bubble if gas is escaping. Never use a naked flame to check for gas leaks. Household soap solutions may cause corrosion and are not suitable.

Question 19: What is the purpose of the Emergency Control Valve (ECV) on a domestic gas meter?

To measure the volume of gas consumed
To allow the gas supply to be turned off in an emergency (Correct answer)
To regulate the gas pressure to appliances
To prevent backflow of gas into the mains

Correct answer: To allow the gas supply to be turned off in an emergency

The Emergency Control Valve (ECV) is a quarter-turn valve fitted to the gas meter that allows the entire gas supply to the property to be shut off quickly in an emergency. When the handle is perpendicular to the pipe, the valve is closed. Only Gas Safe registered engineers or National Gas Emergency Service operatives should operate the ECV on the upstream side of the meter.

Question 20: What is the risk if a decommissioning purge is not carried out before dismantling a gas connection?

Residual gas will only cause appliance malfunction, not explosion
Residual gas in the pipe will escape when the connection is broken, creating an explosive atmosphere that can be ignited by any nearby ignition source (Correct answer)
Gas disperses instantly so no purge is needed before disconnecting
Only a minor smell of gas — not enough to cause explosion

Correct answer: Residual gas in the pipe will escape when the connection is broken, creating an explosive atmosphere that can be ignited by any nearby ignition source

Any residual gas in disconnected pipework will escape when the connection is broken. If sufficient gas accumulates and meets an ignition source (sparks, flames, static), it can ignite explosively. Decommissioning purge removes this risk.

Question 21: What is the minimum distance a balanced flue terminal must be from an opening window, air vent, or other opening into a building?

100 mm
200 mm
600 mm
300 mm (Correct answer)

Correct answer: 300 mm

A balanced flue terminal must be positioned at least 300 mm from any opening into a building, including openable windows, air vents, and doorways. This separation prevents combustion products from being drawn back into the building. Specific distances may vary depending on the appliance rating and flue type — always refer to the manufacturer's instructions and BS 5440-1.

Question 22: Why is it dangerous to simply turn on the gas supply without purging new pipework?

Air in the pipework only causes the appliance to fail to light — no explosion risk
Air is harmless and purging is an optional precaution
New pipework contains only clean air so purging is not necessary
Air trapped in the pipework mixes with incoming gas, creating a potentially explosive air-gas mixture that could ignite when the appliance attempts to light (Correct answer)

Correct answer: Air trapped in the pipework mixes with incoming gas, creating a potentially explosive air-gas mixture that could ignite when the appliance attempts to light

Air remaining in new or repaired pipework mixes with incoming gas to create an air-gas mixture within the explosive range. If an appliance attempts to ignite this mixture, an explosion can result. Purging eliminates this risk.

Question 23: What is the legal requirement regarding notification of gas work to local authority building control?

All gas work must be notified within 48 hours
Gas work by Gas Safe registered engineers is self-certified and notified through the Gas Safe notification scheme (Correct answer)
No notification is ever required for gas work
Only work over £5,000 in value needs notification

Correct answer: Gas work by Gas Safe registered engineers is self-certified and notified through the Gas Safe notification scheme

Gas Safe registered engineers can self-certify their own work under the Building Regulations competent persons scheme. The work is notified to local authority building control through the Gas Safe Register notification system, removing the need for separate building control approval.

Question 24: What action must be taken if a tightness test reveals a pressure drop?

Trace and locate the leak(s), repair, then re-test to confirm tightness before proceeding with any gas work or restoring supply (Correct answer)
Report to the gas transporter and await instructions
Increase the test pressure to identify the leak location
Re-test after 24 hours as pressure drops can be due to temperature change

Correct answer: Trace and locate the leak(s), repair, then re-test to confirm tightness before proceeding with any gas work or restoring supply

Any pressure drop during a tightness test indicates a leak. The leak must be traced (using suitable leak detection fluid or an electronic gas detector), repaired, and the tightness test repeated to confirm the installation is gas-tight.

Question 25: When installing a vertical flue from a gas boiler through a flat roof, what is the minimum height the flue terminal must extend above the roof surface?

600 mm (Correct answer)
150 mm
At least 250 mm above the highest point of the roof penetration
300 mm

Correct answer: 600 mm

A vertical flue terminal passing through a flat roof must extend at least 600 mm above the roof surface. This height ensures adequate dispersal of combustion products, prevents the terminal from being blocked by debris or ponding water, and reduces the risk of flue gases being drawn back into the building through nearby openings.

Question 26: What does a yellow or orange flame on a natural gas burner indicate?

The correct operational colour for a gas burner
High gas pressure causing excess fuel combustion
Incomplete combustion — insufficient air supply causing carbon particles to glow as the flame burns luminously (Correct answer)
The appliance is in its warm-up phase and will correct automatically

Correct answer: Incomplete combustion — insufficient air supply causing carbon particles to glow as the flame burns luminously

A natural gas burner should produce a predominantly blue flame. A yellow or orange flame indicates incomplete combustion due to insufficient air, producing luminescent carbon particles (soot) and CO.

Question 27: How often must a landlord arrange a gas safety check on appliances in a rented property?

Every 6 months
Every 24 months
Only when a new tenant moves in
Every 12 months (Correct answer)

Correct answer: Every 12 months

The Gas Safety (Installation and Use) Regulations 1998 require landlords to have gas appliances, fittings, and flues checked at intervals of not more than 12 months by a Gas Safe registered engineer. A Landlord Gas Safety Record (LGSR) must be issued after each check.

Question 28: What is the purpose of a CO alarm in a domestic property?

To automatically shut off gas appliances when CO is detected
To measure the efficiency of gas appliances for service purposes
CO alarms are only required in commercial properties
To provide early warning of CO accumulation before dangerous concentrations are reached, allowing occupants to evacuate (Correct answer)

Correct answer: To provide early warning of CO accumulation before dangerous concentrations are reached, allowing occupants to evacuate

CO alarms provide an audible warning when CO concentrations rise, giving occupants time to evacuate before reaching dangerous levels. They are the only way to detect CO, which has no smell or colour.

Question 29: What is the function of a flame supervision device (FSD) on a gas appliance?

To provide ignition sparks to the burner
To adjust the flame height for efficiency
To shut off the gas supply to the burner if the flame is extinguished, preventing a gas escape (Correct answer)
To control the room temperature

Correct answer: To shut off the gas supply to the burner if the flame is extinguished, preventing a gas escape

A flame supervision device (FSD), such as a thermocouple, flame rectification probe, or mercury vapour capsule, monitors the presence of a flame at the burner. If the flame is extinguished for any reason, the FSD closes the gas valve to prevent unburnt gas from escaping into the room. This is a critical safety device on all modern gas appliances.

Question 30: What component must be fitted where a gas flue pipe passes through a combustible material such as a timber floor or wall?

A gas isolation valve
A pressure relief valve
A fire-resistant sleeve with a minimum 25 mm air gap (Correct answer)
A condensate trap

Correct answer: A fire-resistant sleeve with a minimum 25 mm air gap

Where a gas flue pipe passes through combustible material (such as a timber floor, ceiling, or wall), a non-combustible fire-resistant sleeve must be fitted. There must be a minimum 25 mm air gap between the flue pipe and the combustible material, filled with non-combustible material if necessary. This prevents heat transfer from the flue igniting the surrounding structure.

Question 31: What dangerous gas is produced as a result of incomplete combustion of natural gas?

Nitrogen dioxide (NO₂)
Sulphur dioxide (SO₂)
Carbon dioxide (CO₂)
Carbon monoxide (CO) (Correct answer)

Correct answer: Carbon monoxide (CO)

Carbon monoxide (CO) is a highly toxic, colourless, and odourless gas produced when natural gas undergoes incomplete combustion due to insufficient oxygen supply. CO poisoning can be fatal. Signs of incomplete combustion include yellow or orange flames, sooting, and increased CO/CO₂ ratios.

Question 32: What is the national gas emergency telephone number in Great Britain?

0800 111 999 (Correct answer)
0345 850 3025
0800 023 1110
999

Correct answer: 0800 111 999

0800 111 999 is the National Gas Emergency Service number, operated by Cadent (and other gas network operators). It is available 24 hours a day, 7 days a week, and is free to call.

Question 33: What is the minimum free area of ventilation required for an open-flued gas appliance with a rated input over 7 kW in a room?

5 cm² for every kW of rated input
5 cm² per kW of rated input above 7 kW (Correct answer)
10 cm² per kW of rated input above 7 kW
No additional ventilation is required

Correct answer: 5 cm² per kW of rated input above 7 kW

For open-flued appliances with a rated input exceeding 7 kW, additional ventilation of 5 cm² of free area per kW above 7 kW is required. The first 7 kW is considered to be served by normal air infiltration in the room. This is specified in BS 5440-2 and Approved Document J.

Question 34: What is the acceptable CO/CO2 ratio in flue gas for a correctly adjusted natural gas boiler?

Between 0.008 and 0.010
Between 0.004 and 0.008
Below 0.004 (Correct answer)
Above 0.010

Correct answer: Below 0.004

A CO/CO2 ratio below 0.004 indicates efficient and complete combustion in a correctly adjusted natural gas boiler; a ratio above 0.004 indicates incomplete combustion requiring investigation.

Question 35: When a chimney serves an open-flued gas fire, what test must be carried out to confirm the chimney is safe to use?

A smoke test (flue integrity test) and spillage test (Correct answer)
A pressure test at 200 mbar
A water flow test
An electrical continuity test

Correct answer: A smoke test (flue integrity test) and spillage test

Before connecting an open-flued gas fire to a chimney, a smoke test (flue integrity test) must be carried out to confirm the chimney is structurally sound and does not leak combustion products. A spillage test must also be performed with the appliance operating to ensure the chimney provides adequate draught and products of combustion are safely evacuated.

Question 36: What is a CP12 certificate in the context of the GSIUR 1998?

A certificate of competence for a specific gas appliance type
A Landlord Gas Safety Record confirming annual safety checks have been completed (Correct answer)
A certificate confirming gas tightness of a new installation
A Gas Safe engineer's registration certificate

Correct answer: A Landlord Gas Safety Record confirming annual safety checks have been completed

A CP12 is the Landlord Gas Safety Record (sometimes called a Gas Safety Certificate), documenting the annual safety check of gas appliances and fittings in rented accommodation, as required by Regulation 36 of the GSIUR 1998.

Question 37: According to current gas industry guidance, how long should an engineer wait after purging before attempting to light an appliance?

10 minutes regardless of appliance type
The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear (Correct answer)
30 seconds while operating the fan to clear the burner area
There is no waiting period — the appliance can be lit immediately after purging

Correct answer: The time specified in the appliance manufacturer's instructions — typically enough time for any residual air-gas mixture near ignition components to clear

The manufacturer's instructions specify the required pre-ignition procedure, which includes any required purge period before attempting ignition. Following the manufacturer's instructions is mandatory under PUWER and the GSIUR 1998.

Question 38: What material must NOT be used for gas pipework installations in the UK?

Steel with threaded joints — only press-fit is permitted
Plastic — all plastic pipework is prohibited for gas
Copper — it is not suitable for gas
Lead — lead pipework is prohibited for gas installations due to its toxicity and poor joint integrity (Correct answer)

Correct answer: Lead — lead pipework is prohibited for gas installations due to its toxicity and poor joint integrity

Lead pipework is completely prohibited for gas installations in the UK. Materials approved for gas pipework include copper, carbon steel, and approved flexible hoses. Each must be joined using appropriate approved methods.

Question 39: Before purging a gas installation that has been disconnected for more than 12 months, what additional step is required?

A full tightness test of the installation before introducing gas, to confirm no deterioration has occurred during the period of non-use (Correct answer)
Contact the gas transporter for permission to reconnect
A visual inspection of accessible pipework only
Simply turn on the gas and purge as normal

Correct answer: A full tightness test of the installation before introducing gas, to confirm no deterioration has occurred during the period of non-use

Pipework that has been inactive for extended periods may have developed leaks due to joint deterioration or corrosion. A full tightness test before introducing gas is essential to confirm integrity before purging.

Question 40: Under RIDDOR, within what timeframe must a dangerous gas fitting be reported to the HSE?

Within 48 hours
As soon as is reasonably practicable (Correct answer)
Within 7 working days
Within 24 hours

Correct answer: As soon as is reasonably practicable

Under RIDDOR, a Gas Safe registered engineer must report a dangerous gas fitting to the HSE as soon as is reasonably practicable. There is no specific fixed deadline in hours, but it should be done promptly — typically the same day or as soon as the engineer has access to the online reporting system.

Question 41: Why must flue terminals be correctly positioned on an external wall or roof?

Terminal positioning is only relevant for aesthetic reasons
Terminal position only matters for boilers over 20 kW output
Terminals must face north to prevent wind-induced back-draughts
To ensure adequate dispersion of flue gases away from windows, doors, and air vents, and to prevent re-entry of combustion products (Correct answer)

Correct answer: To ensure adequate dispersion of flue gases away from windows, doors, and air vents, and to prevent re-entry of combustion products

Flue terminals must be positioned to ensure combustion products disperse safely without re-entering the building through windows, doors, or ventilation openings. Document J of the Building Regulations specifies minimum clearance distances.

Question 42: When installing gas pipework, what is the minimum distance it should be kept from electrical cables where they run parallel?

150 mm
10 mm
25 mm (Correct answer)
50 mm

Correct answer: 25 mm

Gas pipework should be installed at least 25 mm away from electrical cables where they run parallel. Where they cross, the gas pipe should ideally pass behind the electrical cable. This separation prevents potential damage from heat and reduces ignition risk in the event of a gas escape.

Question 43: What is an 'Emergency Control Valve' (ECV) in a domestic gas installation?

The isolation valve at or near the gas meter that can shut off the entire gas supply to the property in an emergency (Correct answer)
The valve between the meter and the service pipe
The valve on an individual gas appliance
A valve operated remotely by the gas transporter

Correct answer: The isolation valve at or near the gas meter that can shut off the entire gas supply to the property in an emergency

The Emergency Control Valve (ECV) is located at or near the gas meter and allows the entire gas supply to the property to be isolated quickly in an emergency. All occupants and engineers should know its location.

ACS CCN1 Core Domestic Gas Safety Assessment

The ACS CCN1 is the UK's core domestic gas safety certification required for Gas Safe Register membership. It covers gas legislation, combustion, ventilation, pipework, flue systems, unsafe situations procedures, and meter controls through written multiple-choice assessments.

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