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Gas interlock systems for commercial kitchens

Updated 23 October 2026 · SEO Dons Editorial

What does a gas interlock do, and why does the gas shut off?

An interlock links the kitchen's mechanical ventilation to the gas supply, so that if the fans stop, the gas stops too. Walsall Council describes the purpose as preventing gas appliances from operating when mechanical ventilation is not running, which reduces the risk of carbon monoxide build-up, oxygen depletion and fire.

HSE gives the reason. A shortage of air, or incorrect flueing, can lead to incomplete combustion and an accumulation of combustion products such as carbon monoxide. Canopies turn this into a system question. A CIBSE Journal training module explains that most appliances under a canopy are designed to run without a flue, but others, such as some convection ovens and deep fat fryers, usually need a dedicated flue and many manufacturers permit them under a canopy instead. The canopy and extract then do the flue's job.

HSE's ventilation sheet says that where extraction serves as the flue, it is considered a flue and requires an appropriate interlocking system connecting the airflow to the gas supply. Regulation 27(4) of the Gas Safety (Installation and Use) Regulations 1998 is the underlying rule for power-operated flues: the system must safely prevent the appliance operating if the draught fails.

This page explains the system. It does not describe gas work, which belongs to a Gas Safe registered engineer.

Who is responsible under the regulations?

The 1998 Regulations are marked for England, Wales and Scotland on legislation.gov.uk. Three duties matter most:

  • Regulation 3: nobody may carry out gas fitting work unless competent, and an employer or self-employed person doing the work must belong to a class approved by HSE. HSE says in restaurants and similar workplaces that means a Gas Safe registered engineer qualified for the work.
  • Regulation 35: every employer must ensure gas appliances, installation pipework and flues at the workplace are maintained in a safe condition.
  • Regulation 34: the responsible person must not use an appliance, or let it be used, if they know or suspect it cannot be used safely.

When an appliance is installed, regulation 33 requires the installer to examine any flue or means of ventilation used with it. HSE's catering FAQ says the law requires safety devices to be maintained too, inspected by a competent person, with annual inspection a reasonable minimum. HSE adds that the employer should check a contractor's Gas Safe identity card.

What does BS 6173 say about interlocks?

BS 6173:2020 is BSI's specification for installing and maintaining gas-fired catering appliances. BSI's public page says it was published on 31 March 2020 and covers new and previously used appliances burning natural gas or LPG, but it does not reproduce the interlock clause. The standard is paid-for, so read the current edition through the installing engineer.

A CIBSE Journal module posted in June 2010 quoted the 2009 edition as requiring appliances to be interlocked with "any mechanical ventilation that is fitted to enable their safe operation". It drew the conclusion that every fan in the kitchen needs to be interlocked, including a canopy over a steamer. That module is old and refers to the previous edition, so treat it as background. One interlock maker's product page still cites BS 6173:2009, which is a reason to ask which edition a certificate refers to.

How does the system prove the fans are running?

PartWhat the sources say
Fan provingOne maker's panel, the Blauberg SIL-1250, verifies fan operation through built-in current monitoring or optional pressure differential switches. The first senses the fan's electrical load, the second senses air movement
Gas valveCIBSE Journal (2010): a gas solenoid valve conforming to BS EN 161, with no manual override
Control panelCIBSE Journal (2010): links valve and ventilation, usually near the fan speed controllers, and can take a signal from emergency gas isolation buttons
Gas provingCIBSE Journal (2010), citing the 2009 edition: where a solenoid valve is used and appliances lack flame supervision, a means of proving all appliances are off before gas is allowed in

HSE is blunt about bypasses: installing manual bypasses on such interlock systems is not permitted. If the gas stops because a fan has failed, the interlock is doing its job and the fault to chase is the fan. The extractor fan guide covers the fan side.

Where do carbon monoxide and carbon dioxide monitors fit?

They are an addition, not a substitute. HSE's gas sheet says that where carbon monoxide alarms are installed they should give an audible alarm and be interlocked to the gas pipework with a fail-safe shut-off that needs manual intervention to restore the supply. It then adds that the alarms are only warning devices, and that the primary safeguard remains an adequate, effective ventilation system.

The CIBSE module describes control panels that can isolate the gas on fan failure and also watch carbon dioxide, carbon monoxide and temperature. It says sensors should be designed for commercial and industrial use, and that monitoring can only support systems that were correctly designed, installed and regularly maintained.

Can an existing kitchen be fitted with an interlock?

HSE says there are large numbers of installations that do not comply with BS 6173 or the law. It accepts that BS 6173 is not retrospective, but tells owners not to be complacent: where there is no interlock, assess whether a risk is likely to arise and, if so, make sure it is prevented or controlled.

Councils are firmer. Argyll and Bute Council says new ventilation systems must be interlocked so that gas cannot be turned on unless the extract is running. Hillingdon Council says all commercial catering establishments must have an interlock. Walsall Council reported on 3 March 2026 that a takeaway had its gas supply disconnected after it was found operating without a working one.

In outline, the systems described above are built from a control panel, a way of proving each fan, a gas valve on the supply and connections to the fan controls. Each step touching the gas supply is Gas Safe work. Restaurants and pubs can read how this sits beside the rest of the kitchen system on the restaurant ventilation page.

How is an interlock tested, and what records should exist?

The test belongs in the engineer's inspection of the appliances, flues and safety devices. A useful record names the interlock, the fans it proves and the date it was tested. Hillingdon's officers say they ask for copies of the gas certificate during routine inspections.

The ventilation itself needs looking after too. HSE notes that effective preventative maintenance and cleaning helps stop nuisance shutdowns when the ventilation system fails, and grease build-up is the usual cleaning issue, covered in the TR19 Grease guide. The wider extract rules are in the kitchen extraction guide, and you can send an enquiry through the form on this site if you want a Gas Safe registered engineer's help.

Sources

Common questions

Why has the gas stopped working when the extract fan is off?

That is what the interlock is designed to do. Walsall Council describes interlocks as preventing gas appliances from operating when mechanical ventilation is not running. Do not bypass it: HSE says manual bypasses are not permitted, so have the fan fault found and fixed.

Does an interlock replace the annual gas safety check?

No. HSE says gas appliances, flues, pipework and safety devices must be maintained in a safe condition and inspected by a competent person, with annual inspection a reasonable minimum. The interlock is one of the safety devices that inspection covers.

Does solid-fuel cooking need the same arrangement?

The gas interlock concerns gas supplies. HSE says solid fuel appliances produce carbon monoxide in normal operation and must have an appropriate extraction system that removes the toxic fumes, and it points to a separate information sheet, CAIS26, for solid fuel in commercial kitchens.

Do the same rules apply in Scotland and Northern Ireland?

The 1998 Regulations are marked for England, Wales and Scotland on legislation.gov.uk, and Argyll and Bute Council in Scotland also expects new ventilation systems to be interlocked. Northern Ireland was not checked for this page, so confirm the position locally.

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