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Kitchen extraction cleaning - interlock diagnostics
A gas interlock cutting the gas mid-service is frustrating - but it may be doing its job, reacting to a genuine loss of extraction airflow. Often, the root cause traces back to dirty extraction: a grease-choked system losing airflow, or a fan failing under grease. Here is when interlock failures trace back to dirty extraction, and why cleaning can be the real fix. This is general information, not gas-safety advice.
The short answer
A gas interlock cutting the gas is often treated as an annoyance or an interlock fault - but it may be a genuine signal, and frequently the trail leads back to the extraction being dirty. Understanding this helps you fix the real problem. This is general information; gas and interlock work must be done by a qualified engineer. How the interlock works (briefly). A gas interlock links the gas supply to the extraction: it only permits the gas to flow while the extraction is running and moving enough air (proved by an air-proving switch or sensor), and it cuts the gas if the extraction stops or the airflow drops below what's needed. So the interlock is, in effect, monitoring the extraction airflow and shutting off the gas if it's insufficient. This means a tripping interlock can be a signal about the extraction. Why dirty extraction trips the interlock. There are two main ways a dirty extraction causes interlock trips: (1) Reduced airflow from grease-choking. A grease-choked extraction (clogged filters, grease-laden ductwork, a strained fan) moves less air than it should - the grease restricting the airflow. If the airflow drops below the threshold the interlock's air-proving requires, the interlock detects insufficient airflow and cuts the gas. So a grease-choked system can trip the interlock simply by not moving enough air. (2) Fan failure or faltering from grease. A grease-strained fan can fail (seize or burn out) or falter (run poorly), stopping or dropping the airflow - which the interlock detects, cutting the gas. So a failing grease-laden fan trips the interlock too. In both cases, the interlock is working correctly - it's detecting a real loss of extraction airflow, caused by the dirty extraction. So the trip traces back to the grease. Reading the signal right. So when an interlock keeps cutting the gas, it's worth considering that the extraction may genuinely be failing - and dirty extraction is a common cause. The interlock isn't necessarily faulty; it may be correctly reporting that the extraction airflow is insufficient (because grease has choked the system or the fan is failing). Misreading this as 'the interlock is playing up' - and especially trying to override or bypass the interlock - would be a mistake: it ignores the real problem (and, in the case of bypassing, removes the safety protection that stops gas cooking with no ventilation). The right response: check and clean. So the right response to a repeatedly-tripping interlock is to have the extraction checked (is it grease-choked? is the fan failing?) and, if so, cleaned - removing the grease to restore the airflow and free the fan. Cleaning can be the real fix, addressing the cause of the trips. A qualified engineer should also check the interlock and air-proving (to rule out or fix any genuine interlock/gas fault, and confirm the diagnosis), since gas and interlock work is theirs - but the underlying cause is often the dirty extraction, which cleaning resolves. So when interlock failures trace back to dirty extraction, cleaning the system is the real fix - not overriding the interlock. So a tripping interlock can point at dirty extraction; clean it. This is general information, not gas-safety advice.
Key points
The interlock watches the airflow
To see why interlock failures can trace back to dirty extraction, start with what the interlock does: it monitors the extraction airflow and cuts the gas if that airflow is insufficient. A gas interlock links the gas supply to the extraction - it only permits the gas to flow while the extraction is running and moving enough air (proved by an air-proving switch or sensor on the system), and it cuts off the gas if the extraction stops or the airflow drops below the required threshold.
So the interlock is, in effect, constantly checking that the extraction is moving enough air, and shutting off the gas if it isn't (to prevent gas cooking with inadequate ventilation - a safety measure). This means a tripping interlock is a signal about the extraction airflow: it trips because it has detected the airflow as insufficient. The question, then, when an interlock keeps tripping, is why the airflow is insufficient - and a common answer is dirty extraction (grease reducing the airflow or a grease-strained fan failing), covered next. So the interlock watches the airflow - it cuts the gas if extraction is insufficient - which is why its trips can point at the extraction's condition. So the interlock trips on insufficient airflow. This is general information, not gas-safety advice.
Grease chokes the airflow
One main way dirty extraction causes interlock trips is by reducing the airflow: a grease-choked system moves less air, and if the airflow drops below the interlock's threshold, the interlock trips. As grease builds up in the extraction - clogging the filters, coating and narrowing the ductwork, and loading the fan - it restricts the airflow (the grease choking the system). So a grease-laden extraction moves less air than it should, and the more grease, the less airflow.
If that reduced airflow falls below the threshold the interlock's air-proving requires (the minimum airflow it's set to confirm), the interlock detects insufficient airflow and cuts the gas - correctly, because the extraction genuinely isn't moving enough air. So a grease-choked extraction can trip the interlock simply by being too choked to move the required airflow. In this case, the interlock isn't faulty - it's accurately reporting that the extraction airflow has dropped (because grease has choked it). Cleaning the system (removing the grease) restores the airflow, so it's above the threshold again, and the interlock stops tripping. So grease chokes the airflow - a grease-laden system trips the interlock - as one way dirty extraction causes interlock failures. So a grease-choked system can trip it. This is general information, not gas-safety advice.
A failing fan drops the airflow
The other main way dirty extraction trips the interlock is through the fan: a grease-strained fan that fails or falters stops or drops the airflow, which the interlock detects. As covered elsewhere, a grease-laden fan is strained (unbalanced and loaded by grease), and a strained fan can fail (seize or burn out) or falter (run poorly, lose performance). When the fan fails or falters, the airflow it drives stops or drops - and the interlock, detecting the lost or insufficient airflow, cuts the gas.
So a failing or struggling grease-laden fan trips the interlock too - and, like the choked-airflow case, the interlock is working correctly (detecting a real loss of airflow, caused by the grease-strained fan). This can present as the gas cutting out when the fan is under strain (perhaps intermittently as the fan struggles, or definitively when it fails). Cleaning the system (removing the grease to free and rebalance the fan) can restore the fan's performance and the airflow - resolving the trips (if the fan hasn't already failed and needs repair). So a failing fan drops the airflow - grease strain trips the interlock too - as the second way dirty extraction causes interlock failures. Between them, grease-choking and fan strain are common grease-related causes of interlock trips. So a grease-strained fan can trip it. This is general information, not gas-safety advice.
Read the signal, don't override it
The crucial thing when an interlock keeps tripping is to read the signal correctly - it may be right - and never to override or bypass it. It's tempting to treat a repeatedly-tripping interlock as 'the interlock playing up' (a fault in the interlock itself) - but often the interlock is working correctly, detecting a genuine loss of extraction airflow (from grease-choking or a failing fan). So the trips may be an accurate signal that the extraction is failing, not an interlock malfunction. Misreading this - assuming the interlock is faulty - can lead to ignoring the real problem (the dirty extraction).
And the worst response is to override or bypass the interlock (to stop the annoying cut-outs). This would remove the safety protection - allowing gas cooking to continue with insufficient (or no) ventilation, which is dangerous (combustion products, including carbon monoxide, building up). So never bypass a tripping interlock. Instead, read it as a possible signal about the extraction, and investigate. A qualified engineer should check the interlock and air-proving (to confirm whether the airflow really is insufficient, and rule out or fix any genuine interlock/gas fault) - but the underlying cause is often the dirty extraction, which cleaning resolves. So read the signal, don't override it - the interlock may be right, pointing at dirty extraction. So heed the interlock; never bypass it. This is general information; gas and interlock work is for a qualified engineer.
Cleaning can be the real fix
So when interlock failures trace back to dirty extraction - a grease-choked system with reduced airflow, or a grease-strained fan failing - cleaning the system can be the real fix, addressing the cause rather than the symptom. If the extraction is checked and found grease-choked or its fan grease-strained, cleaning it (removing the grease to restore the airflow and free the fan) removes the cause of the interlock trips - so the airflow returns above the threshold, the fan runs freely, and the interlock stops cutting the gas. The problem is resolved by cleaning, not by fighting the interlock.
This reframes a frustrating interlock problem as, often, an extraction-cleaning problem: the interlock was correctly reporting that the extraction had become dirty and was failing, and cleaning fixes that. So rather than repeatedly resetting the interlock, calling it faulty, or (dangerously) overriding it, the sound response is to have the extraction checked and cleaned - which can resolve the trips at their source. A qualified engineer confirms the interlock and gas side (and fixes any genuine interlock/gas fault, or repairs a failed fan), while a competent cleaner cleans the extraction - together addressing the real cause. So cleaning can be the real fix - address the cause, not the symptom. When an interlock keeps tripping, consider the extraction, and have it cleaned. So clean the extraction to fix the cause of the trips. This is general information, not gas-safety advice; gas and interlock work is for a qualified engineer.
Questions
It cuts the gas when it senses the extraction isn't moving enough air - so repeated trips can mean the extraction is genuinely failing, often from grease-choking or a failing fan. A gas interlock links the gas to the extraction, cutting off the gas if the extraction stops or the airflow drops below the required threshold (a safety measure to stop gas cooking with inadequate ventilation). So an interlock that keeps tripping may be correctly detecting insufficient extraction airflow. A common cause is dirty extraction: a grease-choked system (clogged filters, grease-laden ductwork, a loaded fan) moves less air, which can fall below the threshold; or a grease-strained fan fails or falters, dropping the airflow. In both cases the interlock is working correctly, pointing at the extraction. So the fix is often to have the extraction checked and cleaned - not to override the interlock. A qualified engineer should also check the interlock/gas side. So it cuts the gas because the extraction airflow is insufficient - often from grease. So because the extraction airflow is insufficient. This is general information, not gas-safety advice.
Yes - a grease-choked extraction moves less air (which the interlock can detect as insufficient), and a grease-strained fan failing drops the airflow - both trip the interlock. There are two main ways dirty extraction trips the interlock. First, reduced airflow: grease build-up (clogged filters, grease-laden ductwork, a loaded fan) restricts the airflow, so the system moves less air - and if it drops below the interlock's air-proving threshold, the interlock cuts the gas. Second, fan failure: a grease-strained fan can fail (seize or burn out) or falter, stopping or dropping the airflow the interlock needs - tripping it. In both cases the interlock is correctly detecting a real loss of extraction airflow, caused by the grease. So yes - a dirty extraction is a common cause of interlock trips, and cleaning it (restoring the airflow and freeing the fan) can resolve them. So yes - grease-choking and fan strain both trip it. This is general information, not gas-safety advice.
No - never override or bypass a gas interlock; it's a safety system, and if it keeps tripping, have the cause found and fixed (often a dirty extraction) by the right professionals. An interlock that keeps cutting the gas is usually detecting a genuine problem (insufficient extraction airflow), so it's a signal to investigate, not to override. Bypassing or overriding it would remove the safety protection - allowing gas cooking to continue with inadequate or no ventilation, which is dangerous (combustion products, including carbon monoxide, building up). So never bypass it. Instead, have the cause diagnosed: a qualified engineer to check the interlock and air-proving (and fix any genuine interlock/gas fault), and the extraction checked and cleaned if it's grease-choked or the fan is failing (often the real cause). So the answer to persistent tripping is diagnosis and repair/cleaning - never override. So no - never bypass it; find and fix the cause. This is general information, not gas-safety advice.
Have both checked - a qualified engineer for the interlock and air-proving, and the extraction for grease-choking or a failing fan; often the extraction is the real cause, which cleaning resolves. A persistently-tripping interlock could be a genuine interlock/gas fault, or (commonly) a real loss of extraction airflow from dirty extraction - so both should be checked to find the cause. A qualified engineer checks the interlock, air-proving and gas side (confirming whether the airflow really is insufficient, and ruling out or fixing an interlock/gas fault). The extraction should be checked for grease-choking (reduced airflow) or a grease-strained/failing fan - often the underlying cause. If the extraction is dirty or the fan failing, cleaning (and any fan repair) resolves it; if it's a genuine interlock/gas fault, the engineer fixes that. So checking both distinguishes the cause - and the extraction is often it. So have both checked; the extraction is often the cause. So check both to find the cause. This is general information, not gas-safety advice.
If the trips are caused by grease-choking or a grease-strained fan (a common cause), cleaning - restoring the airflow and freeing the fan - can resolve them; if the fan has already failed or it's a genuine interlock fault, further repair is needed. Where the interlock is tripping because the extraction is grease-choked (reduced airflow) or the fan is grease-strained (dropping the airflow), cleaning the system addresses the cause: removing the grease restores the airflow above the interlock's threshold and frees the fan to run properly - so the interlock stops tripping. So cleaning can be the real fix in these common cases. However, if the fan has already failed (seized or burnt out), it needs repair or replacement as well as cleaning; and if the trips are actually a genuine interlock or gas fault (not the extraction), a qualified engineer must fix that. So cleaning stops the trips when dirty extraction is the cause - which a check confirms. So yes, if dirty extraction is the cause. So cleaning fixes it when grease is the cause. This is general information, not gas-safety advice.
A qualified (Gas Safe registered) engineer for the interlock and gas side, and a competent extraction cleaner for the extraction; gas and interlock work is the engineer's, cleaning the grease is the cleaner's. A tripping interlock spans two areas, each needing the right professional. The interlock, air-proving and gas side are gas work - so a qualified, Gas Safe registered engineer must check and fix any interlock or gas fault (and confirm whether the airflow really is insufficient). The extraction - if grease-choking or a failing fan is the cause - is cleaned by a competent extraction cleaner (removing the grease to restore the airflow and free the fan). So the two work together: the engineer on the interlock/gas, the cleaner on the extraction. The kitchen operator should not attempt gas/interlock work, and must never bypass the interlock. So a qualified engineer handles the interlock, a competent cleaner the extraction. So a gas engineer and a cleaner, each their part. This is general information, not gas-safety advice.
A gas interlock that keeps cutting the gas may be reacting to a grease-choked extraction or a failing fan. We clean the whole system to restore the airflow and free the fan - often the real fix for the trips, addressing the cause not the symptom. Ask us to check and clean your extraction. This is general information, not gas-safety advice; interlock work is for a qualified engineer.
