What Is a Gas Interlock System in a Commercial Kitchen?

A gas interlock system is a safety control that links the gas supply in a commercial kitchen to the mechanical extraction, so gas cannot reach the cooking appliances unless the extraction fans are running. If the fans stop, fail or are switched off during service, a valve on the gas supply closes and the appliances go out. The point is simple: gas cooking produces carbon monoxide and other combustion products, and in a busy kitchen the canopy extraction is what carries them away. Without it, those gases build up where staff are working.

How a Gas Interlock Works

An interlock watches the extraction system and holds a gas valve open only while it is satisfied that air is moving. When it loses that signal, it shuts the gas off.

Most systems have three parts. A sensor proves the extraction is working, usually by measuring air pressure or airflow in the ductwork, or by monitoring the current drawn by the fan motor. A control panel reads that sensor. An automatic valve on the kitchen gas supply, normally a solenoid valve, opens only when the panel allows it. Many panels also carry an emergency stop button, so staff can cut the gas to the whole kitchen from one place, and some include a gas proving function that checks for an open burner tap or a leak before the supply is restored. Some kitchens also have carbon dioxide monitoring linked to the same panel, which shuts the gas off if the air quality in the kitchen gets too poor.

Which Kitchens Need One

A commercial kitchen with gas cooking appliances and mechanical extraction is generally expected to have its gas supply interlocked with that extraction. It is a requirement of the British Standard for gas catering installations, BS 6173, for new installations and for kitchens that are altered or refitted.

That covers restaurants, takeaways, cafes, pubs, hotels, and the kitchens in schools, care homes and offices. The design of interlock devices is also covered by the gas industry standard IGEM/UP/19, which the engineer installing or checking one will work to. What the law itself says is broader: under the Gas Safety (Installation and Use) Regulations 1998, whoever controls the premises must keep gas appliances, pipework and flues in a safe condition. The interlock is one of the ways a catering installation meets that duty.

Older kitchens are where the questions come up. A kitchen fitted before the current standard may not have an interlock at all. Whether that is recorded as a defect on your safety check depends on the installation, the ventilation and what has been changed since it went in, and the engineer will explain their reasoning on the report. What rarely changes is the outcome when a kitchen is refurbished, extended or re-equipped: expect the interlock to be fitted as part of the work.

Why a Gas Interlock Trips

An interlock that cuts the gas is usually doing its job: it has lost the signal that the extraction is working. The cause is normally in the ventilation, not the gas.

• Fans switched off or not started. The most common cause. The extraction has to be running before the gas will open.
• Blocked or greasy filters. Heavy grease build-up reduces airflow until the sensor no longer reads it as enough.
• A failing fan, belt or motor. The fan may still be turning but not moving enough air.
• A faulty sensor, tube or panel. Pressure tubes can split or clog with grease, and panels can fail like any other electronics.
• The emergency stop has been pressed. The gas stays off until the panel is reset.
• A gas proving failure. On systems with proving, an appliance tap left open or a leak on the pipework stops the gas coming back on.

Staff can confirm the fans are running and use the panel's reset as the manufacturer intends. Anything beyond that needs an engineer. Never bypass, bridge or wedge an interlock to keep cooking. It removes the protection that stops combustion gases building up in the kitchen, and it will be found at the next check.

How the Interlock Is Checked Each Year

The interlock is tested as part of the annual gas safety inspection of a commercial kitchen, which produces a catering gas safety record, often called a CP42. The engineer proves that the gas shuts off when it should, not just that it opens.

A proper test switches the extraction off, or simulates a loss of airflow, and confirms the valve closes and the appliances go out. The engineer checks that the emergency stop cuts the gas, that the reset works, and that any gas proving function detects an open tap. The same visit covers the appliances themselves, the flame supervision devices, the gas pipework and the ventilation. Our commercial gas safety certificate page sets out what the CP42 inspection includes, and our guide on how often commercial gas appliances should be serviced covers the timing.

Keeping the Interlock Working Between Checks

Most interlock problems start with the extraction, so the best maintenance is keeping the canopy and ductwork clean. A kitchen that looks after its extraction has far fewer nuisance trips.

• Clean or replace canopy filters on the schedule your extraction contractor recommends, more often in a heavy frying kitchen.
• Have the ductwork and fans cleaned and serviced by a ventilation specialist, and keep their reports with your gas records.
• Make sure every member of staff knows where the emergency stop is and what it does.
• Write down each unexplained trip with the date and time. A pattern helps the engineer find the cause.
• Book the gas safety check early enough that any remedial work on the interlock can be done before the record expires.

When You Need an Engineer, and Who to Call

Call a Gas Safe registered engineer with commercial catering qualifications if the interlock trips with the fans running, will not reset, or has been damaged. Call your ventilation contractor if the fans themselves are the problem.

The two trades overlap here, and it is common for each to point at the other. An engineer can prove whether the interlock panel, sensor and valve are working; if they are, the fault is in the extraction. If your kitchen is being refitted, bring the gas engineer in at the design stage so the interlock, gas proving and emergency stop are planned rather than added at the end. For an inspection or a fault visit, send us your kitchen's appliance list and a description of the problem and we will quote before any work is booked.