Fitting a gas leak detector

In the price list this item covers the labour to mount and connect one gas leak detector. It typically includes:

• choosing the location and height according to the type of gas and the manufacturer's instructions,
• fixing the mounting plate or bracket to the wall and securing the detector,
• connecting the power supply to suit the detector type, via a plug-in socket, a fixed supply or a control panel,
• where the detector is linked to a valve or panel, connecting the signal cable to the output relay,
• switching on, waiting for the sensor to warm up and carrying out a function test with the test kit specified by the manufacturer,
• explaining to the owner what the lights and alarm tones mean.

The work does not include the detector itself, the solenoid valve, new cable runs through the property, any work on the gas pipework or a gas safety inspection. Fitting a valve into the pipework is a separate job for a gas engineer. If the pipework also needs to be altered or extended, see the page on gas pipe relocation and connection.

• Gas hob or cooker in the kitchen. The most common situation. A burner left on unlit or a loose connection hose are classic causes of a leak.
• Boiler in a flat or house. A detector near the boiler watches for leaks at the gas connection and fittings.
• Plant room or utility room. Here a detector is often combined with a valve that cuts off the supply when the alarm goes off.
• Rented property. Landlords fit one as a precaution, since they cannot control how tenants use the hob.
• LPG from cylinders or a bulk tank. Typical in rural homes off the gas grid, park homes, holiday lodges, caravans and boats. This gas is heavier than air and collects at floor level.
• After gas pipework alterations. When new pipework is run or an appliance is moved, it is a good moment to add a detector.

In an ordinary home a gas leak detector is usually a voluntary safety measure. In commercial kitchens, larger plant rooms and some special appliance locations, gas detection or a gas safety interlock may be required by the design or by the relevant regulations. In that case the designer or the gas engineer decides on the type and wiring.

This is the most important decision, both when buying and when fitting. Mains natural gas is mostly methane. It is lighter than air and rises towards the ceiling when it escapes. LPG, that is propane or butane from cylinders and tanks, is the opposite: it is heavier than air, stays close to the floor and flows into lower spaces such as cellars, voids and drains.

Manufacturers therefore usually specify mounting about 30 cm below the ceiling for natural gas and about 30 cm above the floor, or lower, for LPG. Detectors are made either for one specific gas or with a setting for both. A methane detector fitted near the floor, or an LPG detector fitted below the ceiling, will pick up a leak late or not at all. When buying, look for a detector certified to the European standard for domestic combustible gas detectors (EN 50194) rather than an unmarked import.

A gas leak detector is not a carbon monoxide alarm. Carbon monoxide is produced by poor combustion, for example when a flue is blocked or an appliance is badly maintained. It is monitored by a different device with different siting rules. With boilers, gas fires and wood burners, both are often fitted.

Fitting one detector is a short job. To avoid delays and make sure the detector ends up in the right place, it is worth sorting out a few things in advance:

• Type of gas. A mains connection means natural gas, a cylinder or tank means LPG. Buy the detector accordingly.
• Type of detector. Decide whether you want an alarm only, automatic shut-off with a valve, or a notification to your phone.
• Power supply. Check whether there is a socket or spur at the right height. A natural gas detector near the ceiling usually needs a new fused spur or a cable run in trunking, because most sockets are low on the wall or just above the worktop.
• Access to the pipework. If a valve is to be fitted, the gas engineer needs clear access to the supply pipe and the emergency control valve at the meter.
• Instructions and paperwork. Have the detector manual ready, and if there is a recent gas safety record or service report for the property, keep it to hand.

If a valve is being fitted, allow for the gas being turned off for a short time. The boiler and hob will not work during the job, so it is better to avoid the coldest days of the year.

Choosing the location

1. Find out which gas the property uses, natural gas or LPG, and check that the detector is designed for it.
2. Choose the room with the appliance and a spot close to it, typically within a few metres of the hob or boiler as stated in the manufacturer's instructions.
3. Set the height, about 30 cm below the ceiling for natural gas and about 30 cm above the floor for LPG.
4. Avoid locations that manufacturers rule out, such as above the sink, next to the cooker hood or extractor fan, near windows and doors, behind curtains, inside cupboards, and in damp or dusty areas.
5. Confirm that power and, where needed, a cable to the valve or control panel can reach the chosen spot.

Mounting

The mounting plate is fixed to the wall using the template supplied. The detector must be held firmly and the sensor vents must not be covered. Adhesive pads should not be relied on, as heat and grease in a kitchen gradually make them come away.

Connecting the power

Detectors come in three common versions. The first plugs straight into a socket, the second is hard-wired to a 230 V supply and the third runs on low voltage from a control panel or power supply unit, typically 12 V. A hard-wired supply, usually via a switched fused connection unit, is a job for an electrician. Manufacturers' instructions for hard-wired detectors generally require a means of isolation that disconnects all live conductors and installation by a competent person. Check with your local building control body whether the electrical part of the work needs to be notified.

Linking to a shut-off valve

If the detector is to cut off the gas when it alarms, a solenoid valve is fitted on the supply. The valve goes into the gas pipework, typically downstream of the emergency control valve, and this part must be done by a Gas Safe registered engineer. After any work on the gas pipework, the engineer carries out a tightness test and records the work. The electrician or detector installer then connects the detector's output relay to the valve following the manufacturer's wiring diagram. With manual-reset valves the gas does not come back on by itself after an alarm, someone has to find the cause of the leak first.

Commissioning and testing

Once switched on, the sensor needs a few minutes to warm up and stabilise. The detector is then tested in the way the manufacturer specifies, using test gas or a test kit. Some manufacturers allow a test with a cloth dampened with alcohol. The installer checks that the alarm sounds and, where a valve is connected, that the valve closes. Finally, the owner is shown what each light and tone means.

• Stand-alone plug-in detector. The simplest option, alarm only. Suitable for a kitchen with a single appliance. Basic plug-in models are widely sold for roughly £15 to £40.
• Detector with relay output. Can control a valve or an extractor fan or send a signal to an alarm system. Manufacturers usually give two alarm stages, for natural gas at around 10 % and 20 % of the lower explosive limit.
• System with a control panel. Several detectors in different rooms and one panel that controls the valve. Used in plant rooms and larger houses.
• Link to a security, telecare or smart home system. The alarm is sent to a phone, a monitoring centre or a telecare service, which is useful for older or vulnerable occupants.

Sensors have a limited service life. Manufacturers commonly state a minimum life of about five years. After that the whole detector is replaced or the sensor is changed as the instructions describe. It is therefore worth writing the installation date directly on the detector.

• Wrong height. A natural gas detector often ends up low on the wall, plugged into a socket above the worktop, simply because that is where the power is. Escaping gas, however, collects under the ceiling.
• Detector for the wrong gas. In a holiday lodge or caravan running on LPG, a methane detector is mounted under the ceiling.
• Detector above the hob or next to the cooker hood. Steam and grease clog the sensor, the extraction dilutes the gas, and the detector either gives false alarms or fails to react.
• Detector inside a cupboard or behind a curtain. The gas does not reach the sensor in time.
• Testing with a lighter. Gas from a lighter can permanently damage the sensor and manufacturers explicitly forbid it.
• Cleaning sprays and solvents nearby. Alcohol, varnish, silicone and aerosols can affect the sensor or trigger the alarm.
• Forgotten service life. The detector has been on the wall for ten years, the green light is on, but the sensor no longer responds as it should.
• Valve fitted without a gas engineer. A solenoid valve is put into the pipework as a DIY job, with no tightness test and no record of the work.

People stop taking a detector seriously if it beeps for no reason, and sooner or later they unplug it. That is why it pays to know the most common causes. Semiconductor sensors react not only to gas but also to certain vapours. An alarm can be set off by nail varnish, alcohol-based cleaners, hairspray, thinners, solvents used when decorating or silicone sealant during kitchen repairs. During cooking, steam and fumes from the pan can also interfere if the detector is too close to the hob.

When the alarm sounds, always act first as if it were a real leak. Only once the room has been ventilated and the cause is clear does it make sense to treat it as a false alarm. If false alarms keep happening for no obvious reason, the sensor may be at the end of its life or the detector may be badly positioned. In that case it should be moved or replaced, not switched off.

A detector that simply plugs into a socket can be positioned by the owner, provided the manufacturer's instructions are followed. A hard-wired 230 V connection or wiring into the consumer unit is work for a qualified electrician, ideally one registered with a competent person scheme. Any work on the gas pipework, including fitting a solenoid valve, must by law be carried out by a Gas Safe registered engineer, and LPG installations require an engineer qualified for LPG and for the type of installation, for example a house, park home, caravan or boat. Inspection and safety checks of gas installations are covered on the page gas safety certificate and inspection. If the boiler is being replaced or connected at the same time, this is handled together with gas boiler installation and connection.

• the detector is designed for the gas used in the property and is mounted at the correct height for it,
• it is close to the appliance, but not above the sink, next to the cooker hood, inside a cupboard or by a window,
• it is firmly fixed and the sensor vents are clear,
• after warm-up the normal operation indicator is lit as described in the manual,
• during the test the alarm sounds and, if a valve is connected, the valve shuts off the gas,
• where the pipework was worked on, you have the gas engineer's record of the work and tightness test,
• the installation date and the recommended replacement date are written on the detector or in the paperwork.

During use, repeat the test as the manufacturer recommends, for example at the annual boiler service. Wipe the detector occasionally with a dry or slightly damp cloth, as described in the instructions, while it is switched off.

1. Do not switch lights or appliances on or off, do not use the doorbell and do not use any naked flame.
2. Turn off the gas at the emergency control valve by the meter if it is safe to do so, but do not go into a cellar to reach it.
3. Open windows and doors to ventilate.
4. Leave the property and, from a safe place, call the gas emergency number: 0800 111 999 in England, Scotland and Wales, 0800 002 001 in Northern Ireland, or for LPG the emergency number of your supplier shown on the tank.
5. Do not turn the gas back on until a gas engineer has found the cause.

The labour price in the NUMIQ price list for fitting a gas leak detector is €35 per unit. This covers labour including small consumables, without the detector itself, the valve or cables. Prices vary by region and city.

The final cost depends on:

• the type of detector, whether plug-in, hard-wired or a system with a control panel,
• the number of detectors and rooms,
• the length and method of the cable run to the power supply and the valve, in trunking or chased into the wall,
• fitting the solenoid valve into the pipework by a gas engineer, including the tightness test,
• linking to a security, telecare or smart home system.

Further related items can be found in the section on gas fitting.