Commercial gas safety · Kent
Commercial Kitchen Gas Interlock Systems Explained
If you run a commercial kitchen with gas appliances, you almost certainly have a gas interlock — and the day it trips is the day you find out you've got one. This guide explains what an interlock is, what trips it, what to check before calling an engineer, and what a Gas Safe engineer does on a service visit.
What a gas interlock actually does
A gas interlock is a safety control that connects your kitchen's extract ventilation system to the gas supply feeding your cooking line. The principle is simple: if the extraction isn't running, the gas won't flow. If extraction stops or drops below a safe airflow, the interlock cuts the gas at the meter via a solenoid valve.
This matters because commercial gas cookers, ranges and combi ovens produce combustion gases — carbon monoxide, carbon dioxide, water vapour, nitrogen oxides — that need to be drawn out of the room. Without working extraction, those gases accumulate. Carbon monoxide is the dangerous one. It's odourless, colourless and at sufficient concentration it kills people.
An interlock is the layer that stops a kitchen from running gas appliances with the extraction off — whether the canopy fan has failed, the make-up air fan has tripped, someone has switched extraction off to "quieten things down", or a pressure sensor has detected the airflow is below the design figure.
If you're a kitchen operator, owner, or facilities manager, the interlock is one of the most important pieces of safety kit you have. Gas Safe engineers consider it non-negotiable for any commercial gas installation. UKLPG and the Catering Equipment Suppliers Association both treat it as standard practice. Your insurer almost certainly assumes you have one, even if it isn't explicitly named in your policy schedule.
How an interlock is built up
A typical commercial gas interlock has four main components:
- Air pressure switch (or current sensor) on the extract fan. Senses whether extraction is actually moving air. The pressure switch is the more rigorous setup — it confirms airflow, not just that the fan motor is drawing current. A current sensor only confirms the motor is electrically alive.
- Air pressure switch on the make-up air (MUA) fan, where one is fitted. Same principle, applied to the supply side. If the MUA fan fails, kitchens go into negative pressure and combustion air starves — extraction loses effectiveness even if it's running.
- Control panel. The brain. Mounted on the wall — usually in the kitchen or just outside it. Lights show extract OK, MUA OK, gas valve open. There's a test button, sometimes a reset, and on most modern panels a fault diagnostic light.
- Gas solenoid valve at the meter. The actuator. Normally-closed: needs power to stay open. If the panel cuts power — because extraction has failed — the valve drops shut and gas stops at the meter. There's no way for a single appliance to override this.
When everything is healthy, the panel keeps the solenoid open and the kitchen runs as normal. The interlock is invisible. You only notice it when something trips.
What trips a gas interlock
In our day-to-day on Kent commercial kitchens, the eight most common interlock trips are:
- Extract fan belt slipping or broken. Motor still running, fan blade barely turning. Pressure switch picks up the airflow drop and trips. Common on older canopies that haven't had belts replaced in years.
- Extract fan motor failure. Bearings gone, capacitor failed, or thermal overload tripping. Fan stops dead. Interlock catches it immediately.
- MUA fan failure. Less obvious because the kitchen can still see extraction running — but the airflow balance is gone and the pressure switch on the supply side trips.
- Grease-clogged filters. Filters loaded so heavily the airflow drops below the pressure switch threshold. The fan is fine, the filters are doing the strangling.
- Pressure switch out of calibration. Pressure switches drift. After a few years they can either trip too early or fail to trip at all. The first is annoying, the second is dangerous.
- Loose wiring at the panel or solenoid. Vibration, heat, age. A loose connection drops voltage to the solenoid and it shuts.
- Solenoid valve coil failure. The coil burns out and the valve fails closed. Common on installations that are 15+ years old.
- Someone has hit the emergency stop or the test button without resetting. Often a new staff member during cleaning. Easy to fix once you know to look for it.
What it never is: the gas appliances themselves. The interlock sits upstream of every appliance. If your combi oven, your six-burner, your grill and your fryer have all lost gas at once, the interlock has tripped. It's not eight simultaneous appliance faults.
What to check before you call an engineer
If your gas has cut out across the whole cooking line and you suspect the interlock, there are four quick checks any kitchen manager can do safely before calling for an engineer attendance:
- Look at the interlock control panel. Note which lights are on, which are off, and which (if any) are flashing or red. This single observation tells an engineer over the phone what's most likely tripped. Take a photo of the panel — it saves time on the call.
- Check the canopy extract fan is running. Walk under the canopy. You should hear it and feel airflow. If you can't, that's almost certainly your problem.
- Check the MUA (supply air) fan if you have one. Usually in a plant room or on the roof. Same test — can you hear it, is it moving air through the supply grille?
- Press the reset on the control panel — once. If the trip was momentary (a brief airflow drop) the system will come back. If it trips straight back out, you have a real fault and an engineer is needed.
What not to do: don't try to bypass the interlock. Don't tape down a pressure switch. Don't unscrew the solenoid coil. Don't run the kitchen on a bottled-gas portable hob because the mains gas is off — that bypasses every layer of safety the building has, and your insurer will not look kindly on it if anything happens. If the interlock is tripping, the safe response is engineer attendance, not workaround.
What to check before you call an engineer
If your gas has cut out across the whole cooking line and you suspect the interlock, there are four quick checks any kitchen manager can do safely before calling for an engineer attendance:
- Look at the interlock control panel. Note which lights are on, which are off, and which (if any) are flashing or red. This single observation tells an engineer over the phone what's most likely tripped. Take a photo of the panel — it saves time on the call.
- Check the canopy extract fan is running. Walk under the canopy. You should hear it and feel airflow. If you can't, that's almost certainly your problem.
- Check the MUA (supply air) fan if you have one. Usually in a plant room or on the roof. Same test — can you hear it, is it moving air through the supply grille?
- Press the reset on the control panel — once. If the trip was momentary (a brief airflow drop) the system will come back. If it trips straight back out, you have a real fault and an engineer is needed.
What not to do: don't try to bypass the interlock. Don't tape down a pressure switch. Don't unscrew the solenoid coil. Don't run the kitchen on a bottled-gas portable hob because the mains gas is off — that bypasses every layer of safety the building has, and your insurer will not look kindly on it if anything happens. If the interlock is tripping, the safe response is engineer attendance, not workaround.
Who's responsible for keeping the interlock working
The legal responsibility for maintaining a commercial kitchen's gas installation — including the interlock — sits with the person in control of the premises. In a leased premises that's almost always the tenant operator, not the landlord, unless the lease specifically says otherwise. We see frequent confusion on this in gastropubs and leased restaurant sites where operators assume "the landlord handles gas" — they usually don't.
Practically, that means the operator needs:
- A current CP42 commercial gas safety certificate, issued annually by a Gas Safe registered engineer with the appropriate ticket for commercial catering work
- The interlock checked and tested as part of that annual visit (not always automatic — ask for it explicitly if it isn't on the quote)
- A record of any interlock trips, with the cause and the fix
- Documentation of any modifications to the gas installation, which includes the interlock wiring
Without this paperwork, an Environmental Health Officer (EHO) inspection or an insurance claim following an incident becomes substantially harder. We've attended kitchens where the operator had no idea when the last gas safety check had been done — that's a serious gap to discover during an inspection.
FAQs
Is a gas interlock legally required in a commercial kitchen?
It isn't named in primary legislation as a standalone requirement, but it's effectively required by the combination of the Gas Safety (Installation and Use) Regulations and current Gas Safe industry standards. Any commercial gas installation in the UK is expected to have one, and a Gas Safe engineer will not sign off a CP42 commercial gas safety certificate on a kitchen that should have an interlock but doesn't. Insurers also assume one is fitted on any commercial gas installation. So while no single piece of statute spells it out, you cannot legally operate a commercial gas kitchen without one in practice.
How often should a gas interlock be tested?
Annually as part of the CP42 commercial gas safety certificate, by a Gas Safe registered engineer with commercial catering experience. We'd also recommend a basic in-house test once a month — press the test button on the panel, confirm the gas cuts, then reset. That catches solenoid issues early and keeps staff familiar with the system.
Why does my interlock keep tripping?
The most common reason in our experience is a worn or out-of-calibration pressure switch on the extract side. Second most common is grease-loaded filters dropping airflow below the design figure. Third is a slipping fan belt that nobody has noticed because the fan is still spinning. All three are routine engineer-attendance fixes and none of them are expensive. Repeated trips that come straight back after a reset are a clear signal not to keep resetting — you need an engineer to attend before something more serious develops.
Can I bypass the interlock if it's tripping during service?
No. Don't tape pressure switches, don't unscrew solenoid coils, don't run an extension lead to the solenoid to keep it open. Anyone doing this is creating a Gas Safe offence, voiding insurance, and putting kitchen staff at carbon monoxide risk. The right response to a tripped interlock during service is to close the gas line, switch to electric prep where possible, and get an engineer out.
Does the interlock cover induction hobs and electric ovens?
No — the interlock only controls gas. Electric appliances are not connected to it. That said, the extraction system above them is the same one, and you'd still want extraction running when electric equipment is producing steam, grease aerosol or heat. The Gas Safe industry expectation is that the canopy runs whenever any cooking appliance is in use, regardless of fuel.
What does an interlock service cost?
An interlock check on its own is a short engineer visit. Most operators have the interlock checked as part of the annual CP42 commercial gas safety certificate, which is a single combined visit. We'd encourage you to call us for a current rate — see our Service Agreement page for predictable annual costing if you'd rather not be quoted per visit.
My kitchen has been here for years without an interlock — is that legal?
It almost certainly isn't compliant with current standards. Older installations sometimes pre-date the universal interlock expectation, but that doesn't grandfather them — current Gas Safe practice is to bring older sites up to standard at the next opportunity. If you're operating a commercial gas kitchen without an interlock, we'd recommend booking a Gas Safe assessment urgently. The cost of retrofitting an interlock is far lower than the cost of an EHO closure or a serious incident.
Related on this site
- Kitchen extraction & gas interlock repairs in Kent — canopy and extract systems, make-up air, interlock testing and DW172 compliance, diagnosed and fixed on site.
- Commercial gas and electric cooking appliance repairs in Kent — our service page for cooking line work, Gas Safe certified.
- Knowledge Hub — the full index of repair and service guides.
- The Advantage Service Agreement — annual cover including CP42 gas safety certification and interlock testing as standard.
Interlock tripping in a Kent kitchen?
We're Gas Safe registered, triple-ISO certified, and 5,000+ engineer call-outs a year tells us this isn't your first interlock issue and it won't be ours either. Same-day attendance across our east and central Kent core zone.