Guide
Gas Interlock Systems in Commercial Kitchens
What is a gas interlock system?
A gas interlock links a commercial kitchen's gas supply to its ventilation, so gas can only reach the appliances while the extract and supply fans are proven to be running. If ventilation stops or fails, the interlock closes the gas valve and cooking stops. That is the interlock behaving correctly.
Why does a gas interlock keep tripping?
Because it is usually right. An interlock reacts to the ventilation, and four of the five common causes sit in the extraction rather than in the gas equipment.
| Cause | What is happening | Whose work |
|---|---|---|
| Extract fan has stopped or slowed | A slipping belt or a failing bearing drops airflow below the proving threshold long before anyone notices the fan sounds different. | Extraction engineer |
| Pressure switch reading low | These sit in a grease laden airstream. The sensing tube blocks, the switch reads low, and the interlock does what it was designed to do. | Extraction engineer |
| Filters are loaded | Restricted filters reduce airflow across the whole system, so the interlock trips even though the fault is up on the canopy. | Extraction engineer |
| Make-up air is not keeping up | If the kitchen is under heavy negative pressure, the extract fan cannot move its rated volume even in perfect condition. | Extraction engineer |
| The interlock itself has failed | Solenoid valve, control panel or CO₂ sensor. Least common of the five, and the only one here that needs a Gas Safe registered engineer, though it is where most people start looking. | Gas Safe engineer |
This is worth knowing before you call anyone. If the fan is quiet, the belt is slack or the filters are black, the interlock is not the thing that needs replacing.
Is a gas interlock a legal requirement?
Where a commercial kitchen uses gas catering appliances with mechanical ventilation, gas should not be available unless the ventilation is proven to be operating. That requirement sits in two documents:
| Document | What it covers |
|---|---|
| BS 6173:2020 | Installation and maintenance of gas-fired catering appliances for use in all types of catering establishments. |
| IGEM/UP/19 Edition 2 | Design and application of interlock devices and associated systems in gas appliance installations. Edition 2 introduced CO₂ monitoring as the minimum for new installations, alongside air pressure differential switching or fan current monitoring. |
Overrides are not permitted. If a gas engineer or an environmental health officer finds an interlock that has been bypassed, it gets recorded as a defect.
Who fixes what
The gas side, meaning the solenoid valve, the gas train and the interlock panel itself, is Gas Safe registered work. We are an extraction contractor and we do not carry it out.
What we do carry out is everything the interlock is reacting to. If your interlock is tripping, the useful first step is proving the ventilation:
- Fan condition, bearings, belt tension and drive
- Filter loading and canopy condition
- Airflow through the duct run
- Whether make-up air is balanced against extract
In most cases that is where the fault is, and fixing it clears the trip without anyone touching the gas equipment.